Projects status for Q4 2014

I'm presently allocated to several other vmware projects that are running up against hard deadlines in January 2015. Because of these resource constraints, I've been forced to remove the time lines from my other projects including the public GitHub facing projects. Both pyVmomi and rbVmomi presently do not have time lines for release anymore. I can't control my velocity on these projects, therefore I can't reliably forecast release time lines.

I will revisit both pyVmomi and rbVmomi in February of 2015 and update the projects respective time lines when I gain clarity on what can be done and how long it will take.

It is important to note that these particular versions of these projects are not officially supported VMware products and do not have purchasable support plans at this time.  I will continue advocating inside VMware for the inclusion of these Open Source projects as part of the over-all product suite and API plans, however, at the moment these are Flings under the VMware labs umbrella.

I have truly relished working on pyVmomi in this very open manner and I'm actively looking for ways to make the best parts of this project parts of every project that I work on. I have already presented to various groups the wonderful lessons we've learned from both pyVmomi and rbVmomi. I feel some of my audiences were truly enlightened by my frank assessments of the lives of both these projects.

That reaction to these experiments encourages me in my pursuit of finding better ways to make impactful software. What every developer should be after is impact, not volume. We should pursue not creating more code, nor more refined code, but creating code that makes a bigger impact with lesser effort. By the term 'impact' I mean various permutations of the words 'useful', 'efficient', 'important', 'delightful', and 'powerful'.

I will post more updates in the first three months of 2015 as I have them. Progress will be quite slow between now and then as I will have to address a number of other duties and deadlines. Happy New Year to you all and I look forward to getting back down to business in 2015.


This week on pyVmomi/rbVmomi

Last week, I took on a high priority task for VMware so my work on pyVmomi and rbVmomi had to move down in priority for me. I'll continue to post regular updates on progress but the velocity will have slowed on both project until I have cleared my higher priority tasks.


  • I have slid out the next release until November 15th
  • I have begun learning how to upstream the github changes into the VMware git repos for rbVmomi
    • we will need to determine the upstreaming process' impact on the public repo
    • I need to get any merge requests peer reviewed by VMware internal folks before proceeding


  • I have triaged 2 new bugs
    • issue 176 is an interesting issue we've seen directly impact integrations like OpenStack, SaltStack, and Ansible. I would like to find a clean answer.
    • issue 180 is a problem I've heard reported before, it has to do with a newer vCenter server speaking to an older ESXi host. The current work-around is to ask the programmer to select a lowest acceptable version number (ie: 5.1) and use that namespace exclusively. The bug reporter has done a good job of breaking down the problem. We need to have a solution that will work robustly and impact client code minimally. EDIT: This issue is only known to impact ESXCLI use at this time
  • I wrote a simple sample for an IRC user today describing how to navigate a virtual machine's hardware devices. The sample is rather straight forward and I was glad to get to write a sample after having neglecting samples for so long
  • I  revisited pyVmomi-tools and started a testing refactor using VCRpy

Thursdays will be my rbVmomi/pyVmomi day and I'll alternate between the projects. This week I spent most of my time on pyVmomi so next week I'll try to focus on rbVmomi.

More next week...


Software Engineering at scale is Social Engineering

This week, I spent time at VMware's HQ in Silicon Valley. I gave a number of talks on my lessons learned with pyVmomi and rbVmomi and gave several calls to action. This week, I'd like to share one of the more profound lessons from the project. It has to do with how tools impact social interactions.

The first social networks were the ones that built software. The Software Development Life Cycle (SDLC) were social actions of developers directed, enabled, and enforced through the software tools that they used. If you take this view of creating software, then you it's natural to view any conflicts between departments or teams of developers as an opportunity to invent and apply new technology.

Let's examine something really interesting and profound about Travis CI that may not even have been intentional. The way that Travis CI shifts responsibilities through a tiny change in how builds are specified. The magic is in that .travis.yaml file and any build system that emulated the .travis.yaml file strategy would exhibit the same magical effects (even without using yaml). To understand the profundity of the change, let's revisit the bad-old-days of Developer Operations for a moment.

On the left, our developer builds some code and designs a build system to build their module. On the right an operations person builds a CI server to match. This process has some issues with it already. First off, the operations person must be told what the developer needs in a CI server. This requires a conversation and frequently its one that the operations person isn't directly incentivized to pay much attention to since this isn't likely to be their primary job.

The Operations person may even feel that their cooperation with the developer is a gift. That comes from the fact that the developer likely isn't in the Operations persons direct line of report and their collaboration is a cross-functional team. What is the Operations person really on the hook for?

Let's assume the previous gift from the Operations person lead to success. There's a working build. Over time the build works and breaks as you would expect. The developer is quite happy to fix their code to repair the build problems. Until one day... the build breaks permanently.

First the developer will try their normal work-around tricks. These won't work. The build environment is operationally broken now because the developer changed a library dependency or some other build criteria. Or, perhaps, our developer is spinning their wheels this effort is pointless, because something in the data center is broken.

What's the problem?

  • if the fault is in the build service we waste time debugging code that isn't broken
  • the developer is helpless to do their job without direct intervention from operations
  • the operations people have no view into when a build is broken because of a service problem
  • Operations may exercise their right to change how the server is running and break the build without notice to the developers

In the most extreme cases, the Operations person is going to be bothered during a crisis. This will result in loss of developer time as they wait on Operations (at best), or it will result in the Developer demanding more services from an already busy operations crew what the Operations person thought was a gift. And, often the timing is terrible. Both parties are blocked from doing their jobs effectively.

I've known at least one developer who would handle this by screaming "This is your job! Do your damn job!" Not only did this not get people to do their "damn jobs" but it also made them defensive viewing development as an enemy to defend against. This developer was not pleasant to be around.

Demanding people do their jobs and threatening their livelihoods doesn't exactly setup a safe place for innovation. Not all of us are high-priced-prostitutes and instead aspire to other motivations. (By the way, if you think I'm talking about you ... I'm not. I'm really really not.) If you find yourself here, start asking how to keep people from feeling like they need pitch-forks and torches.

Let's tear down this conflict. What are the facts in this scenario?

  • The developer specifies the build's operational requirements
    • building software is their job
    • running build servers is not their job
  • The operations person runs the build server
    • running workloads, servers, and Infrastructure is their job
    • deciding how software is built is not their job
Does this about cover it?

With these facts consider the following:
  • The developer 
    • can't build software without asking for permission from operations
  • Operations can't create the build server on their own
    • ops has to stop a dev and ask for direction
This is an issue of Separation of Concerns ... only on social systems, not software systems. The concern of specifying a build in most CI systems rests with a separate configuration. In Jenkins this configuration is commonly run through a control panel. That panel is not version controlled, it's not tested code, yet it is effectively a software artifact.

Enter .travis.yaml

The Travis CI build setup is minimal. Point a Travis job at a repository and branch. The configuration work typically carried by an Operations person (those long configuration forms) is carried by the .travis.yaml file. This file is versioned with the code-base itself. That means, when the developer exercises their right to change their own build, the yaml file goes through version control and we can see if things break because of the change in build specification.

We now have two options as the developer:
  1. modify our build to fit current expectations
  2. request a new build environment that fits our new needs
The .travis.yaml file does not eliminate conflict or eliminate the problem, it frames the issue in a different manner. 

Using a build specification by configuration file model means, the build configuration is now part of the project it describes. We have placed the control and authority over that process in the correct place ... with the person who's responsibility it is to maintain it. So one possible conflict is removed, the developer no longer has to beg and wait on Operations to donate their time to allow the developers to do their jobs.

The other part of this new social reality is, if we build a .travis.yaml file that our CI can't support we know it will fail. What's the conversation we're going to have now? The developer now has highlighted boldly that Operations is prepared to give certain services but not others and to ask for new services is to ask someone to go beyond their normal duties.

Operations persons now equipped with the right back-end tools can see what kinds of build requests are coming in, what their resource consumption and performance profiles look like... and without having to interfere with the developer's jobs they can tune their environment to cope. Build configuration by document now becomes a workload specification that an IaaS or a PaaS operator can judge for themselves whether or not they can service.

The conflict and struggle is still there, but now it's framed properly. We accomplish this through software. And, this ability to shape social interaction through software tools is why Software Engineering with more than a handful of people who know each other personally is really Social Engineering.


This week in pyVmomi & rbVmomi


  • version 1.8.2 is live on rubygems
  • release notes are here


I'm in Silicon Valley next week for an unrelated project so it will likely be a slow week on the *Vmomi projects. If folks would like to meet up I'm trying to organize a hack-night for projects in pyVmomi or rbVmomi while I'm in town. Contact me for details.


This week in pyVmomi & rbVmomi


Not much motion this week. I've spent the majority of the week focused on coming up to speed on rbVmomi. Of note we did have a bug report of sockets getting left open and I'll be spending quality time debugging that next week.

  • The next major revision of pyVmomi is slipped to December now in light of my new work commitments. I will keep github up to date on how these projects are going.
  • Disconnect doesn't close socket is this a pervasive bug or a quirk? TBD I'll carve time from my schedule next week to attempt to reproduce and resolve the bug as either a quirk or create a fix. The fix will go in 2014.2 at minimum but might be bad enough to cut 2014.1.2 if needed.
  • We need some more education and evolution on tasks. I've shelved my work on pyvmomi-tools temporarily while I come up to speed on rbVmomi. But, tasks are one of those areas I feel the raw API is too rich for new developers to grasp right away. Some syntax sugar should help.
  • Currently stalled on my desktop is an effort to introduce an SMS "plugin" (plugin isn't the right word but it's close) which I wanted to introduce through pyvmomi-tools. I'll ask for review inside VMware and from key thought leaders in the python and pyVmomi communities before shipping it to pypi ... more on this as we have time.
  • We changed version conventions yet again. On pyVmomi we wanted the version number to communicate freshness and compatibility. So the year-dot-quarter method was used. Then releases moved to every six months so it's 1st half and 2nd half now. Then we found out `-` means something in pypi so now it's just a `.` character. Finally we have and to indicate 1st half of 2014 bug fix 1 is compatible with vSphere 5.5.0. Part of this is we still don't know precisely how pyVmomi github and pyVmomi vSphere will interact on a code-base level going forward. That's TBD be the vSphere teams in charge of that. The admittedly complex interaction between these two things 


Just coming up to speed on the modern state of Ruby gem management since it's been a number of years since I've had to work with them. I'm also moving cautiously since there's a standing development practice and tradition in place that I need to be mindful of.

  • A prerelease for rbVmomi 1.8.2 is available on rubygems now please test!
  • A regular release for 1.8.2 will happen October 1st barring any negative testing results
  • A 1.8.3 release is tentatively set to got to pre-release October 17th (or so) depending on how well we can manage the process of upstreaming pull requests and this is very tentative. Note: this is a change I had intended to hold the release 2 weeks for myself to gain familiarity first. Instead I like this pre-release, delay for 3rd party testing/review, then release strategy and I'll likely adopt it as my normal operating style from now on.
  • Long term planning will have to happen for a 1.9.1 release but I'll not comment much on that until I know what my long term relationship to the project looks like.
  • I opened a low priority research ticket for [higher performance XML](https://github.com/vmware/rbvmomi/issues/57) which seems to be a minor scalability problem rbVmomi faces. My initial research is in the ticket. It's a help wanted item so feedback is much appreciated.
  • NOTE: any item I tag 'help wanted' is an area I feel a 3rd party can either easily help with (usually also tagged 'low hanging fruit') or an area we can't really move on without outside help.
  • NOTE: any item I tag 'VMware staff assistance needed' is something that I feel a 3rd party should probably avoid working on since the issue is fuzzy and bleeds into VMware internal technical details, decisions, or other issues muddy the ticket such that it's not going to move without someone (usually me) bridging the Open Source and VMware internal engineering communities.

General Status

My Friday posts will probably take this two part pyvmomi then rbvmomi flavor as long as I'm bridging both communities. Sorry if that confuses things but that's a function of Conway's law and at the moment the Open Source to VMware and back communications conduit is basically me for both projects so you have to expect a bit of that.

Thanks for your support! The following freenode IRC channels will at least have my IRC 'bot in them #pyvmomi , #pyvmomi-dev , #rbvmomi , #rbvmomi-dev , #govmomi , #govmomi-dev and I'll eventually see IRC messages in those channels through my 'bots. The -dev channels are for advanced programming topics while the other channels will be open for newblings and will need community support since I'm pretty bad at dealing with neophyte level problems these days.

More on each of these threads as progress is made...


On the topic of rbVmomi

Earlier this week I started helping out on the rbVmomi project. My involvement is just to help take some pressure off of Christian Dickmann around reviewing and releasing the next version of rbVmomi.

Compared with pyVmomi, the rbVmomi project has a longer history in Open Source. While pyVmomi has existed longer, rbVmomi has the benefit of being designed from the ground up for the type of collaborative effort an API binding like this can represent. I'll want to be cautious and observant of that established project workflow and primarily act as an accelerant for the processes already there.

To address the initial problem of there being no release this year, I've begun drafting v1.8.2 which should be ready for release in a few days. Having learned from pyVmomi, I've set up a follow up release v1.8.3 to try and catch anything we miss in the earlier release. The follow up release should hit in mid-October if we need it. If it turns out we don't or can't hit mid-October I'll drop the milestone and we'll move to long-term planning. Future release schedules are TBD.

For pyVmomi, this means my attentions are divided and I've shifted out milestones for that project to match my expectations. The second release of 2014 for pyVmomi is now tentatively set for mid-December. (I hope that pyVmomi reaches feature parity with rbVmomi by that release.) Our big additions for the next release of pyVmomi should be SMS and SPBM API support provided we don't hit any hidden issues. We'll hopefully have time for EAM as well.

My role on rbVmomi at this time is just to assist in the current release plan. Christian is very much still the lead developer. I'll be using tags on the open issues and pull requests to help decide what to call out for Christian's direct attention. There's also a bit of process for this project that I'll need to work out on the fly.

More on these topics as things happen...


How to use Conway's Law for good and not evil

If you've been paying attention to our github repository you'll have noticed some noise around the following API additions to pyVmomi...
These are all presently scheduled for the next major release of pyVmomi which is currently set for December of 2014 and will be called 5.5.0-2014.2 barring any major issues.

I'll be working with the various feature teams inside VMware to figure out how best to Open Source their existing API bindings. More importantly, I'll be work with these teams to find a way that allows the effect described in Conway's Law to function beneficially on this set of projects.

In other words, pyVmomi isn't one large project with one BDFL directing the entire API. The reality is that the APIs potentially exposed by pyVmomi are in fact the result of multiple collaborating teams. Each of these teams will tend to be their own unique snowflake.

Couple this with the fact that we will also have the opportunity to leverage contributions from interested third parties, vendors, and partners and you can see that the previous monolithic structure might not survive the strain. I'll be taking some vital time to implement at least one or more extension strategies for the library and have them evaluated. This will probably cost 3 or more weeks worth of time but it will be worth the pain because these are long-lived projects with minimum life-spans on the order of 3 or more years.

As part of this research I've come back time and again to a talk by Doug Hellmann titled Dynamic Code Patterns.

Not to diminish Doug's work at all, but his Stevedore project is an implementation of the Extensibility Pattern which is itself part of the previous generation's Software Design Patterns movement. The design patterns technique came under understandable criticism for not really contributing much to programming and more than occasionally over complicating things. It's these concerns about over complication that are going to slow me down a bit. After all, making things simple is not easy and my goal is to make things as simple as possible and no simpler.

The Stevedore project does offer something to a library like pyVmomi. It is a tool to create extensions. The term 'plugin' is not really accurate when we're talking about modules like SMS. The SMS module is neither a driver, nor is it a hook, but it is an extension. These are new classes and methods that provide new capabilities from the primary facade of the pyVmomi library itself. You can call these plugins but not in the normal sense.

There is also danger in approaching the problem of extending into these new API as a plugin. It quite possibly introduces the problem of turning pyVmomi into a framework and such a transformation would be wholly inappropriate. In particular, I am considering the use case for pyVmomi as a helper library to deliver a driver for SaltStack. What happens to the outer project if pyVmomi itself becomes a framework and does this make those consumer projects unnecessarily more complex?

We want extensibility but not at the cost of adding the need to be aware of more details. We want the library to appear as a unit even though it is actually composed of multiple sub-units. That's something that requires some subtlety. It's not something to bother with if we don't need it so... why do I think we need it?

Over the next 2 weeks I'll be experimenting with SMS support provided in a couple of different ways in the hopes of finding a sustainable, flexible, and robust mechanism to use Conway's law as a means of enforcing a structure of collaboration between teams. In particular there's a set of existing organizational and structural relationships that I feel the current design violates..

In particular, at VMware, I do not personally manage, dictate, or control what the structure or design a given ... feature interface (or sub-API) looks like. It's impractical to think I could. My role is to act as a bridge between VMware and the developer communities interested in building software on-top of the VMware platforms.

Some details about the practical nature of how modules like SMS, SPBM, and EAM for use in pyVmomi are produced directly informs our library design considerations. For example...

  • Feature teams (and their management)
    • design, maintain, and release their own API
    • dictate what API are official, unofficial, and deprecated
    • have their own schedules, priorities, and deadlines
    • are fundamentally disinterested in low-level concerns
Knowing this, any design I create for pyVmomi that dictates that a feature team must talk to me first and then convince me to do things a certain way are very likely to fail. Why? Well, let's take the opposite approach as a thought experiment and see what happens.

If I were to decide that I was going to tightly control pyVmomi and force feature teams to first get approval for API from me before I clicked my big "approved" button and there by uploading their API to github that would mean I could conceivably derail their priorities or deadlines. 

What do you think would happen? I could cause a vital product or feature to slip it's release; I could force an unnecessary conflict between managers; I could find my project usurped by something the feature team felt could disentangle themselves from my meddling in their affairs. Any or all these and other scenarios could happen. In short, I would create an unnecessary friction and unintentional power-struggle as people tried to focus on issues wholly unrelated to something as trivial as providing API to people like yourself.

So, if I want to instead create a successful project in this environment I have to engineer my software so that it can function with the natural (and proper) social boundaries already present. The structure of the code itself will also influence how social interactions occur around the code base. And finally, the modularity of the code will allow me to potentially delegate power, authority, and autonomy to other people.

So what are our design concerns?
  • For feature creators adding to pyVmomi we should,
    • leverage existing library features
    • hide low-level concerns
    • allow independent ownership
    • simplify the process of creating a binding as much as possible
  • For integrating developers working with pyVmomi in their separate projects we should,
    • present a single unified "surface" for them to use
    • hide accidental complexity but expose essential complexity
    • follow a rule of least surprise
I admittedly may think of more as I work through the problems but this captures what we're after in a nutshell. This library in the world of Conway's Law represents a bridge between multiple parties and it's structure will end up reflecting how these groups relate. The pyVmomi software sitting between these groups will be least painful to work with for everyone if it can be molded to it present reality.

After we tackle Open Sourcing these three new API I'll have a better picture of what that reality is. And, that's what large-scale software development is really about, not as much computers and code so much as people, relationships, and communication. Our tools affect our lives and better tools make better lives.

More on this another time...


Developer Community Engagement

If you've not been following along at home, pyVmomi was run in a different manner from most VMware Open Source projects. It's been a bit of a social experiment. The last two weeks since our release, I've been working on distilling lessons learned from the past five months of the project.

I did not plan on also looking into rbVmomi ... but ... at the same time just after VMworld a certain blog post started making the rounds on social media. It's clearly an opportunity to examine what we're doing at VMware around OpenSource development projects.

rbVmomi is a more typical VMware fling project. These start as a developer driven POC project and these are developed on a best-effort basis. The rbVmomi project has closed 6 issues and closed 10 pull requests during its entire lifetime as a VMware project.

pyVmomi has benefited from having my attention full time since April/May of 2014. The total number of issues closed to date is 59 with a total number of 70 merges. These differences in numbers shouldn't be surprising, that's to be expected when you go from free time development to full time development. My personal stats have become quite impressive due to the full-time activity on GitHub.

That's all nice for me, but, what does that really mean for the library? What does that mean for developer use, experience, and over-all for VMware? It's a matter of audience and SDK adoption.

Over on stackoverflow, you can see that in its entire life-span rbVmomi has had 9 questions asked as of this writing. That indicates 9 times people who are likely to seek help on stackoverflow have sought help and those 9 times only 4 of those questions got answers.

Taking a look at the same search for pyVmomi yields 24 questions over a much shorter life-span. 

13 of these questions have been answered and 19 of times people voted on the questions where as with rbVmomi no one voted. If you take a closer look, 17 of those questions occur after my full time commitment to the project. In the shorter time-frame my public commitment and effort to the library has helped increase developer engagement with the library improve by an order of magnitude.

The next question is... is this effort worth it? And how do we determine that

I'm open to suggestions. What else should I be looking at?


This week: Retrospectives

This was a short week, so I would like to take a moment and reflect on where we've been since May.

This week I've been getting ready for a creating a set of new spikes around a few of our unanswered sample requests. Out of these will come my development plan is to create new features to include in pyvmomi-tools. By the way, if you're new to the projects or haven't been following along, part of the reason for breaking out pyvmomi from pyvmomi-tools is to allow us to develop different release cycles and development standards and styles. It would allow a quicker-turn around on some items and also allow some experimentation in pyvmomi-tools that we might not want to risk in the core pyvmomi library.

This is all part of a social experiment I'm conducting trying to help VMware at large find the best way to engage with the open source communities. Earlier in the week someone called out this negative reaction in the rbVmomi community. Ironically, rbVmomi is much older, more robust, and feature complete than pyVmomi but the community reception to pyVmomi has been much warmer in recent weeks.

I'm getting reports of a number of python projects shifting from other vSphere API bindings to pyVmomi as the confidence in the library grows. I've been getting almost nothing but positive feedback from users of the library and I think we're well on our way to becoming the best way for integrators to work with vSphere. And, we're reaching that goal by encouraging better developer practice.

From some IRC chats earlier in the week I found out that at least one shop has traded from vijava to pyVmomi running in jython. I've not tested or verified jython for use with pyVmomi but I'm encouraged to hear the work is progressing well. If anyone else is attempting this kind of work I would appreciate hearing and/or reading about the experience.

I also find this language switch curious because vijava is actually quite well done. As a side note I am doubly curious because of my own past involvement in alternative languages for the JVM. I've not attempted jython with Java hybrid projects before and I'm curious as to how and why these fit together.

 I'll be presenting these stories to VMware teams to help build the case for this style of community engagement and I plan on having a series of discussions around rbVmomi as well. As I've mentioned multiple times in this blog, merely building pyVmomi up is only one of the objectives toward my much larger goal of helping change the way we write software for the cloud.

Part of that larger goal is testing, process, and engagement.

More on this next time...


pyVmomi v5.5.0-2014.1.1 - bug fix - is available from pypi.

This week was VMworld and we still managed to release a quick turn-around bug-fix release for pyVmomi. Up on pypi right now is the v5.5.0-2014.1.1  release. Part of the changes made involved improving our release process and incorporating feedback from RPM and DEB package maintainers.

If you're still using the December release, here's a unified change list between 5.5.0 and 5.5.0_2014.1.1:

  • Simplifies test-requirements.txt
  • Introduces support for tox
  • Changes version number scheme
  • Fixes README to be pypi compatible
  • Improved sdist and bdist packaging support
  • Changes to package information based on The Python Packaging Authority instructions
  • Fix bug that produces traceback when running tests for the first time

Far and away, working on the pyVmomi has been one of the most professionally satisfying projects of my career. That's chiefly because of how immediate the interaction and feedback from users of pyVmomi has been. In most other projects feedback from users of your code base has to navigate its way back to you over time, instead on pyVmomi the feedback has been immediate.

Part of this is due to the ease of public interaction that tools like github, freenode, pypi, and twitter (with ifttt automations) offers. I plan on evangelizing this working-style to other teams within VMware and your positive feedback can only help. For a developer it's a very rewarding way to work and hopefully for a customer it's also very satisfying.

Next week, I'll be working on our 2014.2 milestone and setting up to make a go at some more community samples. It should be noted that while pyVmomi itself is able to run just fine on Python 3, many of the samples are written assuming Python 2.7 ... this is fine since the two projects are decoupled.

The reason we keep the community samples repository separate from the core pyvmomi project is to allow for each project to exercise its own standards. The samples project is very loose while pyVmomi is run extremely tightly. That's a function of where on the stack each project lives. In general the deeper down the stack you go, the more rigid the project needs to run to ensure quality and stability for all the projects built on top of it.

More on the community project next week...


pyVmomi: preparing for 5.5.0-2014.1.1 our first bug fix release.

I've been heads down this week, so a short update this time.

Last week, we released pyVmomi 5.5.0_2014.1 to pypi. This week we started work on preparing RPM and Debian packages which will allow pyVmomi to be included with Linux distributions important for OpenStack work.

Having released 2014.1 I opened a milestone for 2014.1.1 as a bug fix release and identified a few smaller quick turn around tasks. We have one known bug and a few minor improvements and changes that we'll have to get in place. (Being right up against VMworld has slowed down a few tasks, but we're still moving rapidly.)

Notably the 5.5.0-2014.1.1 release will:

  • Fix a bug with sending date-time stamps to the server
  • Tweak the version number standard to fit better with pypi and RPM.
  • Standardize packaging for the pyVmomi library
  • Improve release documentation and processes for versions.
I got a bit side-tracked this week as I investigated more of the pyVmomi internals and noted that the XML documents are non-deterministically assembled. This means from one run to the next the SOAP message coming out of pyVmomi can be different in certain trivial ways.

I noted that...

  • The order of xmlns="*" attributes inside tags can occur in random order
  • The amount of whitespace in documents can vary in some situations
This meant that naive string-based comparisons done in vcrpy's built-in body request matcher can't actually compare XML document contents for logical consistency. I wrote the start of an XML based comparison system but after burning more than three days on the problem I have to stop and wonder if this is worth the effort and if it wouldn't be simpler to just figure out why pyVmomi creates random ordered XML and then fix that instead.

In the next week-or-so, we should be able to deliver a quick-turn around bug fix release with the improvements I've listed here. We're doing well for this now that we're getting more attention from last week's release. The 2014.2 is tentatively scheduled for November 15th this year.

More on these topics next week...


pyVmomi version 5.5.0-2014.1 is available.

Earlier today with help from other VMware employees and #python IRC users, I pushed the buttons necessary to release pyVmomi version 5.5.0-2014.1 to the general public. This is the first open source community built and released version of the vSphere Management API library since VMware open sourced the project in December.

This release featured contributions from 13 contributors, 10 of which were completely unaffiliated with VMware. With the exception of myself the most active contributors are not at all affiliated with VMware.

Special Thanks to...

Thanks as well to William Lam for championing our project as well.

This release marks an important step for pyVmomi, most notably the ability to use pyVmomi with vcrpy means we can do much more in-depth and thorough bug reporting for 3rd party developers. It also means that the focus of development can move from infrastructure to feature parity.

More on that next time...


On the topic of Goals and Objectives for pyVmomi

As long as I'm working on the pyVmomi project, its goal will be to become the single best way to talk to vSphere technologies. This is a broad and hard to measure thing, and with luck as VMware technologies evolve, it's also a moving target. Once we arrive at one location there will be a new version to sail toward. In order to steer accurately, we must set a course by some kind of metaphorical guiding star, and this is what objectives are meant to be.

While the goal is the destination we are sailing our metaphorical ship toward, our near-term objectives are the metaphorical stars we choose to help guide us toward that goal. Just as sailing a ship may require course corrections, which implies choosing different stars; so too might managing a project require course corrections which implies choosing different near term objectives. When we course-correct ourselves, our projects, our teams, or our careers, we are changing the objectives much as a ship navigator might choose a different guiding star at different times during a ships journey toward a distant destination.

In common parlance, the terms goal and objective are virtually synonymous but it makes sense to make a distinction between them when we're talking about conducting the daily business of building software. Being "the best" is kind of hard to measure, it implies quality, adaptiveness, and nimbleness in the library as well as a breadth of uses for the library. This requires us to choose some guiding stars with wisdom.

How do you design a library for these attributes? How do you pick the correct guiding stars?

A little philosophy

A little philosophy is necessary to guide how we go about setting our objectives to achieve our goals. Just a little philosophy is necessary, too much and we spend our days navel gazing, too little and we flail about wildly wondering why we work so hard and accomplish so little. Regular periods of slack followed by pressure are best for this. Creativity can only come when you are free to explore but productivity only really truly solidifies itself under threat of deadline.

So what are some philosophies I could hold in this case?

A few contrary points of view

I might think that audience size is the best measure of project success. That might mean I would have less priority on other aspects of the software and more on things that make the software appeal to a wide audience. In other words, a bug's priority only matters as a measure of the number of new users it can net.

Examples of projects guided by this principle to the exclusion of others might include things like PHP. The design choices in PHP were early on driven by getting broad adoption and rapidly securing mind-share. Very little time was spent thinking about the long-term impact of design decisions. The result is PHP is the most successful programming language (in its niche) of all time and one of the most hated.

I might choose to believe that 'feature count' was a better measure for project success. If I believed that cranking out code was the way to 'get stuff done', then I would probably believe that anything that got in your way of 'getting stuff done' was a waste of time. That would probably mean I would be after the largest volume of code in the shortest amount of time. More code means more function right?

The problem with this is feature creep. If you want to keep a light nimble software project that can respond quickly to changes in its environment a small modular project is best. You keep the project itself small or suffer the consequences. There's usually an 80/20 rule for features and following it can result in faster release cycles.

After years of working on software systems big and small, with tiny audiences and accidental audiences of millions, I've come to believe a few things.

In Generalities

 I feel that the competition between Xbox versus Playstation in the marketplace is a good case-study of these philosophical disagreements in action. The results have mostly played out in the marketplace for us all to study. If we take a lesson from this history we might be able to improve our own state of practice.

In 2012 it was hard to tell if there was a marketplace winner in the video game console market. The three top video game consoles of the time period had traded top position on various metrics repeatedly but by Q2 2014 there is a clear winner in market sales (only time will tell if this is a permanent state of affairs).

Sony had always invested in a complete engineering package for its consoles and frequently talked about 10 year plans with its ecosystem. Ironically, this same business strategy had failed them before. When it came to BetaMax versus VHS this same strategy of 'technical superiority' did not pay off, however, and that's a cautionary tale. The entire engineering process matters.

When building a system you have to take into account all the pertinent forces shaping its market share. These include multiple product audiences, shareholders, and customers, as well as multiple engineering considerations about how the product functions. Not the least of which includes the process by which you create the product itself.

Engineering Objectives

Audience size matters, feature count matters, and perceived quality matters. Each affects the other and each affects the total impact of your software project. Minmaxing on only one dimension or another doesn't necessarily equate to a lasting victory. So we need to find ways to incorporate all these elements into our daily choices. That's what setting objectives is all about.

Over the years, I've been thoroughly impressed at how products generated by very bad engineering can sometimes capture and dominate markets when very good engineering fails. I believe the problem comes from improperly balancing objectives. A single dimension of engineering and design has been maximized at the expense of balancing concerns. It's far too easy to make an easy to measure metric, set it as an objective, and steer the metaphorical ship by a star that has nothing to do with the goal. Such engineering produces something that is arguably beautiful yet broken.

Broken Strategy

For example, a typical strategy used to solve quality issues in software systems is to increase test coverage. Coverage is an easy number to measure. It makes nice charts and gives a wonderful feeling of progress to developers. It's also a trap.

Merely increasing code coverage does not universally improve the code in all its dimensions. In fact, improperly applied test coverage can create tightly coupled systems that are worse suited. This is perhaps the starkest lesson you can learn about successfully reaching a 100% code-coverage goal: you can end up with more technical debt not less. (I could call out certain open source projects here but I won't for brevity's sake.)

If no metric can measure this concept of tight coupling to balance the code coverage metric, then, merely measuring code coverage percentages pushes the software design in the wrong direction. Your team will optimize for coverage at the expense of other attributes. One of those attributes can actually be code quality (in that fixing a simple bug can take an inordinately long time) and flexibility (in the sense that your code can lose the ability to respond to new requirements).

I have come to believe Test Driven Development just as code coverage can also become a trap. Improperly applied, it similarly optimizes systems for unit tests which may not reflect the real design forces that the unit of code is under. These circumstances the code developed can end up very far from the intended destination just as high code coverage numbers can degrade actual quality of a software system.

Actively Compensating

Agile methodologies were intended as a tool to compensate for this dis-joint between the steering stars of objectives and the actual destination. The ability to course correct is vital. That means one set of objectives are perfect for a certain season while the same objectives might be completely wrong for another season.

To effectively use these tools (agile or otherwise) you can't fly by instrument. You need to get a feel for the real market and engineering forces at play in building your software product. These are things that require a sense of taste and refined aesthetics. You don't get these from a text book, you get them from experience.

My experience has taught me that you actually don't want to write more code you actually want to write less. You want to accomplish as much as possible while writing as little code as necessary without falling into code golf. That means that the most effective programmer may have some of the worst numbers on your leader board. Negative lines of code might be more productive than positive, fewer commits may be more profound than more. The mark of good engineering is doing a great deal with very little and that's what we strive for in software engineering.

From Philosophy to Concrete Objective

In the case of pyVmomi, we have no open sourced tests that shipped with version 5.5.0 as released from VMware's core API team. (Note: there are tests but they are fenced off from public contributors and this is a problem when it comes to getting quality contributions from the general population.) With no unit tests available it is almost impossible for a contributor to independently determine if their change positively or negatively impacts the project's goals. Some over-steer in the area of code coverage would be forgivable.

I also want to avoid solidifying library internals around dynamic package and class creation as well as internal aspects of the SOAP parser and its details. This puts me in an awkward position because the simplest most naive way to fence off units and begin busting-gut on test coverage would also force the tests to tightly couple onto the classes currently defined in what long-time pyVmomi developers refer to as the pyVmomi infrastructure.

Separation of Concerns

The fact that there is even a term 'pyVmomi infrastructure' means that there is an aspect of the library that some people need to talk about separately from some other aspect of the library. That indicates a conflation of separate concerns. This particular point in itself would be a lovely talking point for a whole different article on how software engineering becomes social engineering after a certain point. To become a highly used, trusted, and distributed library; pyVmomi should disambiguate these concerns. But, I digress.

Application of Philosophy as Strategy

I spent no less than three weeks developing the test strategy for pyVmomi that will allow us to test without boxing in the library itself. The strategy leans heavily on fixture based testing and specifically on the vcrpy library. In our case, the nuance is that our fixture needs to setup a fake socket with all the correct information in it to simulate an interaction with vCenter and/or ESXi without requiring mocked, stubbed, or simulated versions of each.

If we avoid testing directly design elements (things like the XML parser itself), and we avoid testing in isolation concerns that are deemed infrastructure versus not-infrastructure, then we are left with testing the API "surface" as exposed by pyVmomi. The unit tests call on the actual symbols we want to expose to developers and these are the API surfaces as I call them. The outermost exposed interface intended for end consumption.

The shape of these fixture-based tests are virtually identical to targeted samples of the API pyVmomi is binding. Given a large enough volume of use-cases these unit tests with fixtures might eventually encompass a body of official samples. Existing as tests means that these samples will also validate the fitness of any changes against known uses of the library.

This strategy effectively retro-fits tests onto the library without locking in design decisions that may not have had very much thought. It frees us to build use-cases and eventually fearlessly refactor the library since the tests will not tightly couple to implementation specifics and instead the tests couple to interface symbols.

Objectives Accomplished

We want pyVmomi to continue to exist long enough that it can accomplish its goal of being the best library for working with vSphere. To survive, we need the library to have a lifespan beyond Python 2. We need the library to allow contributors to objectively measure the quality and fitness of their own contributions so it attracts enough developers to evolve and spread toward its goal.

So far we've accomplished the following objectives in the up-coming release due to come out in mere days:
  • Python 3 support gives the pyVmomi library time to live and flexibility to grow
  • Fixture based tests give users and contributors confidence to develop while also...
    • avoiding design detail lock-in
    • hiding irrelevant library infrastructure details
    • providing official samples based on actual API units that will not break as the API changes
  • we also established contribution standards

Objectives to Accomplish

While we want pyVmomi community samples to evolve unrestricted and rapidly, it is also the source for requirements for the library. The samples project is separate so that it can welcome all comers with a low barrier to entry. But, it is very important as it will feed the main pyvmomi project in a very vital way. The samples become the requirements for pyVmomi.

The samples and the pyvmomi unit tests need not have a 1-to-1 relationship between sample script and test, but each sample should have a set of corollary unit tests with fixtures that give basic examples and tests for the use case illustrated in the parent sample. That means one sample might inspire a large number of unit tests.

These are some of the high level objectives to reach going forward on pyVmomi:
  • remain highly reliable and worthy of trust
    • cover all major vSphere API use cases in unit tests with fixtures
    • squash all high priority bugs rapidly which implies releasing fixes rapidly
  • reach feature parity with all competing and cooperating API bindings
To reach these new objectives we'll need to do some leg work to find way-points along the way. We may change some of our finer targeted objectives later, but these objectives help us reach the goal of being so good nobody working in this space can ignore us, being so good we deserve the title the best.

More on that in a future post...


Notes on Developing pyVmomi itself.

Most of my development work over the last few weeks has been spent finding more efficient ways to develop pyVmomi itself. The problem with networked libraries is that they sit between metal and user code.
As I've pointed out before, virtually all code written in the modern world fits in this model. There's a 'core system' under the code you are writing... that is to say the code you write orchestrates some other system of libraries, then you test the core system by writing tests that anticipate what the 'user' of your library is going to do. This is basically API development, at least in spirit.

Everyone does API development (somewhat)

The interesting thing is that in today's world virtually all development is API development if you allow for this loose interpretation of what an API is. The 'user' code may end up being a Selenium test or a unit test. The 'user' party may be yourself or your coworkers ... or they maybe the industry at large. If code gets reused then that code is essentially part of the vocabulary of an API.

I advocate that you write one test per use-case to describe each of the types of anticipated use of your API. These tests define the surface of the library and you should have no distinction between the library's tests and it's public API. That means anything private or internal should only be tested indirectly if it exists at all.

Porting pyVmomi to Python 3

In the case of porting pyVmomi from python 2.x to python 3.x (as I covered in this 3 part post) the problem has been finding a way to rapidly regression test the library on python 2.x and python 3.x interpreters. The technique I settled on was using fixtures for testing.

To build these fixtures I alluded to what I call the simulator problem. In this situation, your back-end is so complex that your stubs and/or mocks become so comparably complex that these fake components approach the complexity of the actual system you are substituting for. At this point, your mock has become a simulator. This is a lot of effort and typically non-unique for any given project. That's why you can find multiple simulators for webservers out there. It makes sense to share effort.

In the vSphere space we have VCSIM which can be used to simulate vCenter. In most situations these simulations will be good enough for writing test cases with fixtures. These test cases with fixtures do not obviate the need for integration testing, but they do shorten the feedback loop for an individual developer. This shorter feedback loop is critical.

Simulating for Success

I recorded a short video this week on how to setup VCSIM. My video is by no means definitive, but I hope it helps get you started. In the video I show how my setup works. I chose to alias my VCSIM to the fake DNS name 'vcsa' and I setup the user 'my_user' with the password 'my_password'. I make thes substitutions so that real IP, usernames, or passwords, do not leak into unit tests. The resulting setup helps me explore the API exposed on the wire by vCenter in my unit tests. Once I hit the scenario I want to develop on I metaphorically freeze it in amber by recording a fixture (as recorded in the preceding video).

Release Plans

I plan on releasing officially the next version of pyVmomi (with python 3 support) in the next 2 weeks. The goal was always to release in front of VMworld. That means we'll be flat-out on the release war-path the next few days until we have a solid, stable, and tested release to push out. Fortunately, we are very nearly there. Python 3 support itself would be a big enough win without any additional changes. The ability to record fixtures in tandem with the library is icing on the proverbial cake and it will help us as a community develop pyVmomi more reliably and uniformly.

In summary

The key to successfully navigating the change from python 2.x to python 3.x is testing, testing, and more testing. The *faster* you can get testing feedback (test, change, retest as a feedback loop) the better off you'll be. Waiting for a CI to kick back results is *far too long* to wait. You want all this to happen in a developer's local development environment. The more *automated* and *stand alone* your tests are the broader the total population of possible contributors are. The standalone test means a CI like Travis CI or Jenkins can run your tests without infrastructure. This does not obviate the need for integration testing but it will hopefully let you catch issues earlier.

If you have a python project on Python 2.x and you want to follow pyVmomi into Python 3, I hope these posts have helped! Now that we have a solid way to test for regression on the library we can start work on feature parity. Future development after the next upcoming release will be focused on building up the library's capabilities.

More on that next time...


What every developer should know about testing - part 3

For the pyVmomi folks in a hurry, this video covers the big shift in the project and the code from the video is here. This week I'll finally dig into some detail on fixture-based testing.


If you don't bother reading more from part 1 and part 2 in this series, the one thing to take away is: testing must be stand aloneautomated, and deterministic no matter what you are writing
No matter what you are doing the bulk of your effort should go toward creating ways to write as little code and as few tests as possible yet still cover the domain. This is  a much harder philosophy to follow than 'cover all the lines' but it is much more robust and meaningful. 

Good code coverage should be the outcome of good testing, not the goal. Because testing is hard and getting it wrong is bad you should write tests as sparingly as possible without sacrificing quality. Finally, unit boundaries are API and you should write tests to reflect the unit boundary which is an art in and of itself.

In part 1 I covered why your testing is bad. In part 2 I covered what are stubs, mocks, and fixture testing. In part 3 we'll get specific and cover how to build a fixture and what it represents as a programming technique.

What your code is determines what your test is.

Virtually all software built today is going to fall into this pattern:
core system -> [your code] -> user's code
Virtually everyone who writes software writes it in a space sandwiched between the software you use and the software that uses you. Interesting things happen when you move up stack far enough that 'user's code' becomes actual human interaction or you move down stack far enough that 'core system' means physics.

In most projects, however, code that has to perform actual human interaction means code written for a web app or some kind of GUI. In these special cases you need tools like Selenium or some other 'bot like Sikuli to drive your tests. In that case the far right of my diagram "User's Code" is simulated in that test framework. It's ultimately code at the end of the day and the code you write for test is something you create anticipating how that middle category "your code" is going to be used.

The more familiar case, where you are sitting between an end-developer (sometimes yourself later in the project's lifecycle) and a core-system of libraries that constitute the framework, runtime, or operating system your code is build on is what most unit test philosophies are build around. This is the world that is most comfortable for mock and stub based testing. It's the world of TDD and other methodologies. But, what happens when you start getting close to the metal when the things we need to mock are on the network or some other physical or transient infrastructure?

This is the case where I advocate the use of fixtures. Depending on what's on the other side of your code the right tool to craft a fixture will differ. I've worked in environments where fixtures had to be physical because we were testing micro-code. Most of the time these days I need a network based fixture.

I am a big fan of vcr, vcrpy, and betamax. These are tools for recording HTTP transactions to create a fixture. In generic terms, a testing fixture helps you fast forward a system to get it into the state you need for testing. In our specific purposes the fixtures replace the need for a network and related network servers.

Recording transactions

BTW: The source code for this test is available on github now.

Here's the sample interaction we want to support. It's a simple set of interactions... we login, get a list of objects, loop through them, and put things away.

    def test_basic_container_view(self):
        si = connect.SmartConnect(host='vcsa',
        atexit.register(connect.Disconnect, si)
        content = si.RetrieveContent()
        datacenter_object_view = content.viewManager.CreateContainerView(
            content.rootFolder, [vim.Datacenter], True)
        for datacenter in datacenter_object_view.view:
            datastores = datacenter.datastore

As written this test goes over the network nine times. Without a tool like vcrpy running this test in any automated way would require us to use a whole pile of cloud infrastructure or at least a smartly built simulator. This means doing special setup work to handle edge cases like faults, or large inventories. It requires the construction of an entire mockup of the production scenario we want to test. This could be automated in itself; but then, if the tool to perform such automations is literally what we're writing; how do we develop and test those automations? That's an extremely time consuming and wasteful yak shaving exercise.

Fortunately, in our project a simple one liner can help us remove the need to always have a service or simulator running somewhere for every test.

                      cassette_library_dir=fixtures_path, record_mode='once')

This decorator allows us to record the observed transactions into a YAML file for later consumption. We can't completely remove the need for a simulator or service, but we can remove the need for such beasts during test.

Modifying Recordings

Once you have the capacity to record network events into a fixture you can tamper with these recordings to produce new and unique scenarios that are otherwise hard to reproduce. That means your code can rapidly iterate through development cycles for situations that are really hard to get the core-system code on that remote server into.

You "shave the yak" once to get a VCSIM to a state that represents the scenario that you want. Then you script your interactions anticipating a use case your end-developer would want to exercise. Finally, using vcrpy decorators, you record the HTTP interactions and preserve them so that you can reproduce the use-case in an automated environment.

Once you have that fixture you can develop, regression test, and refactor fearlessly. You can synthesize new fixtures approximating use cases you might never be able to reliably achieve. And that's how you take something very chaotic an turn it into something deterministic.

This is of course predicated on the idea that you have a VCSIM setup for testing, more on that next time...


What every developer should know about testing - part 2

The short version of this post:

pyVmomi contributions from this point forward will be required to follow this pattern. They include a fixture based unit test build around vcrpy.
Note: While these posts are python specific, the techniques I advocate are not. If you happen to be working in a JVM language, then I recommend Betamax. And, if you happen to be on Ruby, then use vcr. The point of any unit test is that it should be stand alone, automated, and deterministic. These posts discuss how to create deterministic and automated tests in situations where people often argue it's impossible to create such tests.


Last week I covered some basics about unit testing. What is a unit? What do you need to test? What don't you? This week we'll dive a bit deeper and cover why a Stub, a Mock, or any other trick may not solve your problems and how we create a unit test where there's arguably no 'unit' only a client.

In this post we'll briefly recap what a unit test is. Then we'll cover stubs and mocks and why they are useful but aren't sufficient. Finally I'll cover fixtures.

If I'm in the mood, I may cover property based testing at some future date ... but that's an intermediate to advanced topic in my book.

Recap: What a Unit Test is, what it isn't

The dividing line between units is 'human hard' because it's not just 'a method is a unit' ... a method very frequently is a unit but then so is a class and there can be hidden classes and methods. I'm advocating a somewhat controversial position based on the back-lash to TDD you'll find around the blogosphere recently. My position in a nutshell is that tests are best defined at 'unit boundaries' which are necessarily abstract borders between software units (and units themselves are a term of art).

What is a good Unit Test?

There is some debate over what makes a good unit test. In general, your tests should be stand alone, automated, and deterministic (and those three words in this context have very precise meanings). This is simple enough when a unit is simple. For example, the canonical roman numeral example is easy enough to unit test.

In the roman numeral example the unit is easily isolated since the concept of a roman numeral does not require the introduction of additional units. This is the most basic tier of unit testing that every developer  must learn.

The next set of techniques are to use Fakes and Stubs, and then later maybe Mocks, and these work as long as system interactions remain relatively simple. But, these are not sufficient tools for your tool box. You have to learn one more trick before you have all the basic tools you'll need for modern development. You need to know how to build fixtures and the resources that go with them.

When to Stub

If your programming language supports interfaces and dependency injection then creating stubs will feel natural to you. If your unit uses several other objects by composition to accomplish it's work, one of the simplest things to do is write a fake version of the objects your unit under test uses.

That means you have to create an object that implements all the methods of the dependent class that your particular test unit will use. The stub will have to cover as many calls as your unit of code uses. If you call on method 'foo' you need to write something that reasonably reproduces the expected output of 'foo'. This is fine when the call number is small, but it can quickly get out of hand. Take for example that someone felt compelled to write an entire fake server in Java.

The fake HTTP server author calls their product a mock server but this is in fact a stub. You have no facility to assert call order, parameters, or the absence of calls.

When to Mock

A mock is not a stub. With a stub you have to provide a stub implementation of all possible call paths and have no facility to later go back and make assertions on call order. If you do, you probably wrote it yourself... and you've probably neglected what your day job really is.

A mock is about coding for expected calls and call order. The problem with doing this with your stub is that you will have to either be organically grow your stub into a mock to get this information (and that's a whole new project worth of complexity) or you'll have to invent a whole system of semaphores and messages to watch for these details.

With mocks, you can assert how a method was called; you can make assessments about call order; you can also assert that there is an absence of calls. This is all very important for you to be able to do in your unit tests. With these tools you can continue to assert that no matter how you evolve your intervening code the units code continues to use it's underlying API within acceptable parameters.

A concrete example is if you are consuming pyVmomi or rbVmomi as your client library bindings, you can mock the calls to the client binding library. If you observe that vim.VirtualMachine's PowerOff method is still called properly even after you refactor your own library then there's no need for a VCSIM to run your tests at the unit testing phase.

Too much of this, however, and you can't make assertions about the code's behavior outside of test. Not to mention that creating mocks and stubs are programming efforts of their own. This can lead to wonderful code coverage numbers, tightly coupled designs, and a frustrating body of work.

Enter the Network

What if you're writing a client library? On the pyVmomi project, that's what we're doing. A highly efficient and specifically tailored API binding in Python for vSphere. How can we unit test something that's intended for use with a networked appliance?


In the case of building tests for networked software, the simulator problem is a common problem. In order to deal with this it's vital to have some tool that can record your interactions then play them back. The ability to deliberately tamper with the interaction recording is vital. There are bound to be states that the complex server or simulator on the other end can't reach.

If you only use a simulator for your tests, then they are by definition not stand-alone. You have to exit the testing context and enter an administration context to build an orchestrate the situation you want to test. This can be costly and it can be a problem very similar to the simulator problem. You will inevitably have to build a complex environment that will harm the determinism of your tests.

Next week, I'll get specific and cover how to build a test with a recording, we'll have to get into details and I'll cover how I use VCSIM to create the basis for complex situations I can't even create in my environment.

More on that next time...