Last weekend, I wrote a more or less casual post on LinkedIn containing the ‘rules’ (it’s more of a list of terms and conditions, really) I set for myself when it comes to using AI. That post received some interesting comments that made me think and refine my thoughts on when (not) to use AI to support me in my work. Thank you to all of you who commented for doing so, and for showing me that there still is value in being active on LinkedIn in between all the AI-generated ‘content’. I really appreciate it. Now, AI and LLMs like ChatGPT or Claude can be very useful, that is, when used prudently. I think it is very important to be conscious and cautious when it comes to using AI, though, which is why I wrote that post. I wrote it mostly for myself, to structure my thoughts around AI, but also because I think it is important that others are at least conscious of what they’re doing and working with. That doesn’t mean you have to adhere to or even agree with my views and the way I use these tools, by the way. Different strokes for different folks. Because of the ephemeral nature of these LinkedIn posts, and the importance of the topic to me, I want to repeat the ‘rules’ (again, more of a T&C list) I wrote down here. This is the original, unchanged list from the post I wrote on February 15: I only use it to support me in completing tasks I understand. I need to be able to scrutinize the output the AI system produces and see if it is both sound and fit for the purpose I want to use it for. I never use it to explain to me something I don’t know yet or don’t understand enough. I have seen and read about too many hallucinations to trust them to teach me what I don’t understand. Instead, I use books, articles, and other content from authors and sources I do trust if I’m looking to learn something new. I never EVER use it for creative work. I don’t use AI-generated images anywhere, and all of my blogs, LinkedIn posts, comments, course material and other written text are 100% my own, warts and all. My views, my ideas, my voice. Interestingly, most of the comments were written in reaction to the first two bullet points at the time I wrote this blog post. I don’t know exactly why this is the case, it might be because the people who read it agree (which I doubt seeing the tsunami of AI-generated content that’s around these days), or maybe because there’s a bit of stigma around admitting to use AI for content generation. I don’t know. What I do know is that it is an important principle to me. I wrote about the reasons for that in an earlier blog post, so I won’t repeat myself here. Like so many terms and conditions, the list I wrote down in this post will probably evolve over time, but what will not change is me remaining very careful around where I use and where I don’t use AI to help me in my work. Especially now that the speed with which new developments in the AI space are presented to us and the claims around what it can and will do only get bigger, I think it is wise to remain cautious and look at these developments with a critical and very much human view.

When I build and release new features or bug fixes for RestAssured.Net, I rely heavily on the acceptance tests that I wrote over time. Next to serving as living documentation for the library, I run these tests both locally and on every push to GitHub to see if I didn’t accidentally break something, for different versions of .NET. But how reliable are these tests really? Can I trust them to pass and fail when they should? Did I cover all the things that are important? I speak, write and teach about the importance of testing your tests on a regular basis, so it makes sense to start walking the talk and get more insight into the quality of the RestAssured.Net test suite. One approach to learning more about the quality of your tests is through a technique called mutation testing. I speak about and demo testing your tests and using mutation testing to do so on a regular basis (you can watch a recent talk here), but until now, I’ve pretty much exclusively used PITest for Java. As RestAssured.Net is a C# library, I can’t use PITest, but I’d heard many good things about Stryker.NET, so this would be a perfect opportunity to finally use it. Adding Stryker.NET to the RestAssured.Net project The first step was to add Stryker.Net to the RestAssured.Net project. Stryker.NET is a dotnet tool, so installing it is straightforward: run dotnet new tool-manifest to create a new, project-specific tool manifest (this was the first local dotnet tool for this project) and then dotnet tool install dotnet-stryker to add Stryker.NET as a dotnet tool to the project. Running mutation tests for the first time Running mutation tests with Stryker.NET is just as straightforward: dotnet stryker --project RestAssured.Net.csproj from the tests project folder is all it takes. Because both my test suite (about 200 tests) and the project itself are relatively small code bases, and because my test suite runs quickly, running mutation tests for my entire project works for me. It still took around five minutes for the process to complete. If you have a larger code base, and longer-running test suites, you’ll see that mutation testing will take much, much longer. In that case, it’s probably best to start on a subset of your code base and a subset of your test suite. After five minutes and change, the results are in: Stryker.NET created 538 mutants from my application code base. Of these: 390 were killed, that is, at least one test failed because of this mutation, 117 survived, that is, the change did not make any of the tests fail, and 31 resulted in a timeout, which I’ll need to investigate further, but I suspect it has something to do with HTTP timeouts (RestAssured.Net is an HTTP API testing library, and all acceptance tests perform actual HTTP requests) This leads to an overall mutation testing score of 59.97%. Is that good? Is that bad? In all honesty, I don’t know, and I don’t care. Just like with code coverage, I am not a fan of setting fixed targets for this type of metric, as these will typically lead to writing tests for the sake of improving a score rather than for actual improvement of the code. What I am much more interested in is the information that Stryker.NET produced during the mutation testing process. Opening the HTML report I was surprised to see that out of the box, Stryker.NET produces a very good-looking and incredibly helpful HTML report. It provides both a high-level overview of the results: as well as in-depth detail for every mutant that was killed or that survived. It offers a breakdown of the results per namespace and per class, and it is the starting point for further drilling down into results for individual mutants. Let’s have a look and see if the report provides some useful, actionable information for us to improve the RestAssured.Net test suite. Missing coverage Like many other mutation testing tools, Stryker.NET provides code coverage information along with mutation coverage information. That is, if there is code in the application code base that was mutated, but that is not covered by any of the tests, Stryker.NET will inform you about it. Here’s an example: Stryker.NET changed the message of an exception thrown when RestAssured.Net is asked to deserialize a response body that is either null or empty. Apparently, there is no test in the test suite that covers this path in the code. As this particular code path deals with exception handling, it’s probably a good idea to add a test for it: [Test] public void EmptyResponseBodyThrowsTheExpectedException() { var de = Assert.Throws<DeserializationException>(() => { Location responseLocation = (Location)Given() .When() .Get($"{MOCK_SERVER_BASE_URL}/empty-response-body") .DeserializeTo(typeof(Location)); }); Assert.That(de?.Message, Is.EqualTo("Response content is null or empty.")); } I added the corresponding test in this commit. Removed code blocks Another type of mutant that Stryker.NET generates is the removal of a code block. Going by the mutation testing report, it seems like there are a few of these mutants that are not detected by any of the tests. Here’s an example: The return statement for the Put() method body, which is used to perform an HTTP PUT operation, is replaced with an empty method body, but this is not picked up by any of the tests. The same applies to the methods for HTTP PATCH, DELETE, HEAD and OPTIONS. Looking at the tests that cover the different HTTP verbs, this makes sense. While I do call each of these HTTP methods in a test, I don’t assert on the result for the aforementioned HTTP verbs. I am basically relying on the fact that no exception is thrown when I call Put() when I say ‘it works’. Let’s change that by at least asserting on a property of the response that is returned when these HTTP verbs are used: [Test] public void HttpPutCanBeUsed() { Given() .When() .Put($"{MOCK_SERVER_BASE_URL}/http-put") .Then() .StatusCode(200); } These assertions were added to the RestAssured.Net test suite in this commit. Improving testability The next signal I received from this initial mutation testing run is an interesting one. It tells me that even though I have acceptance tests that add cookies to the request and that only pass when the request contains the cookies I set, I’m not properly covering some logic that I added: To understand what is going on here, it is useful to know that a Cookie in C# offers a constructor that creates a Cookie specifying only a name and a value, but that a cookie has to have a domain value set. To enforce that, I added the logic you see in the screenshot. However, Stryker.NET tells me I’m not properly testing this logic, because changing its implementation doesn’t cause any tests to fail. Now, I might be able to test this specific logic with a few added acceptance tests, but it really is only a small piece of logic, and I should be able to test that logic in isolation, right? Well, not with the code written in the way it currently is… So, time to extract that piece of logic into a class of its own, which will improve both the modularity of the code and allow me to test it in isolation. First, let’s extract the logic into a CookieUtils class: internal class CookieUtils { internal Cookie SetDomainFor(Cookie cookie, string hostname) { if (string.IsNullOrEmpty(cookie.Domain)) { cookie.Domain = hostname; } return cookie; } } I deliberately made this class internal as I don’t want it to be directly accessible to RestAssured.Net users. However, as I do need to access it in the tests, I have to add this little snippet to the RestAssured.Net.csproj file: <ItemGroup> <InternalsVisibleTo Include="$(MSBuildProjectName).Tests" /> </ItemGroup> Now, I can add unit tests that should cover both paths in the SetDomainFor() logic: [Test] public void CookieDomainIsSetToDefaultValueWhenNotSpecified() { Cookie cookie = new Cookie("cookie_name", "cookie_value"); CookieUtils cookieUtils = new CookieUtils(); cookie = cookieUtils.SetDomainFor(cookie, "localhost"); Assert.That(cookie.Domain, Is.EqualTo("localhost")); } [Test] public void CookieDomainIsUnchangedWhenSpecifiedAlready() { Cookie cookie = new Cookie("cookie_name", "cookie_value", "/my_path", "strawberry.com"); CookieUtils cookieUtils = new CookieUtils(); cookie = cookieUtils.SetDomainFor(cookie, "localhost"); Assert.That(cookie.Domain, Is.EqualTo("strawberry.com")); } These changes were added to the RestAssured.Net source and test code in this commit. An interesting mutation So far, all the signals that appeared in the mutation testing report generated by Stryker.NET have been valuable, as in: they have pointed me at code that isn’t covered by any tests yet, to tests that could be improved, and they have led to code refactoring to improve testability. Using Stryker.NET (and mutation testing in general) does sometimes lead to some, well, interesting mutations, like this one: I’m checking that a certain string is either null or an empty string, and if either condition is true, RestAssured.Net throws an exception. Perfectly valid. However, Stryker.NET changes the logical OR to a logical AND (a common mutation), which makes it impossible for the condition to evaluate to true. Is that even a useful mutation to make? Well, to some extent, it is. Even if the code doesn’t make sense anymore after it has been mutated, it does tell you that your tests for this logical condition probably need some improvement. In this case, I don’t have to add more tests, as we discussed this exact statement earlier (remember that it had no test coverage at all). It did make me look at this statement once again, though, and I only then realized that I could simplify this code snippet to if (string.IsNullOrEmpty(responseBodyAsString)) { throw new DeserializationException("Response content is null or empty."); } Instead of a custom-built logical OR, I am now using a construct built into C#, which is arguably the safer choice. In general, if your mutation testing tool generates several (or even many) mutants for the same code statement or block, it might be a good idea to have another look at that code and see if it can be simplified. This was just a very small example, but I think this observation holds true in general. This change was added to the RestAssured.Net source and test code in this commit. Running mutation tests again and inspecting the results Now that several (supposed) improvements to the tests and the code have been made, let’s run the mutation tests another time to see if the changes improved our score. In short: 397 mutants were killed now, up from 390 (that’s good) 111 mutants survived, down from 117 (that’s also good) there were 32 timeouts, up from 31 (that needs some further investigation) Overall, the mutation testing score went up from 59,97% to 61,11%. This might not seem like much, but it is definitely a step in the right direction. The most important thing for me right now is that my tests for RestAssured.Net have improved, my code has improved and I learned a lot about mutation testing and Stryker.NET in the process. Am I going to run mutation tests every time I make a change? Probably not. There is quite a lot of information to go through, and that takes time, time that I don’t want to spend for every build. For that reason, I’m also not going to make these mutation tests part of the build and test pipeline for RestAssured.Net, at least not any time soon. This was nonetheless both a very valuable and a very enjoyable exercise, and I’ll definitely keep improving the tests and the code for RestAssured.Net using the suggestions that Stryker.NET presents.

This blog post is another one in the ‘writing things down to structure my thinking on where I want my career to go’ series. I will get back to writing technical and automation blog posts soon, but I need to finish my contract testing course first. One of the things I like to do most in life is traveling and seeing new places. Well, seeing new places, mostly, as the novelty of waiting, flying and staying in hotel rooms has definitely worn off by now. I am in the privileged position (really, that is what it is: I’m privileged, and I fully realize that) that I get to scratch this travel itch professionally on a regular basis these days. Over the last few years, I have been invited to contribute to meetups and conferences abroad, and I also get to run in-house training sessions with companies outside the Netherlands a couple of times per year. Most of this traveling takes place within Europe, but for the last three years, I have been able to travel outside of Europe once every year (South Africa in 2022, Canada in 2023 and the United States in 2024), and needless to say I have enjoyed those opportunities very much. To give you an idea of the amount of traveling I do: for 2025, I now have four work-related trips abroad scheduled, and I am pretty sure at least a few more will be added to that before the year ends (it’s only just February…). That might not be much travel by some people’s standards, but for me, it is. And it seems the number of opportunities I get for traveling increase year over year, to the point where I have to say ‘no’ to several of these opportunities. Say no? Why? I thought you just said you loved to travel? Yes, that’s true. I do love to travel. But I also love spending time at home with my family, and that comes first. Always. Now, my sons are getting older, and being away from home for a few days doesn’t put as much pressure on them and on my wife as it did a few years ago. Still, I always need to find a balance between spending time with them and spending time at work. I am away from home for work not just when I’m abroad. I run evening training sessions with clients here in the Netherlands on a regular basis, too, as well as training sessions in my evenings for clients in different time zones, mainly US-based clients. And all that adds up. I try to only be away from home one night per week, but often, it’s two. When I travel abroad, it’s even more than that. Again, I’m not complaining. Not at all. It is an absolute privilege to get to travel for work and get paid to do that, but I cannot do that indefinitely, and that’s why I have made a decision: With a few exceptions (more on those below), I am going to say ‘no’ to conferences abroad from now on. This is a tough decision for me to make, but sometimes that’s exactly what you need to do. Tough, because I have very fond memories of all the conferences and meetups abroad I have contributed to. My first one, Romanian Testing Conference in 2017. My first keynote abroad, UKStar in 2019. My first one outside of Europe, Targeting Quality in 2023. They were all amazing, because of the travel and sightseeing (when time allowed), but also because of all the people I have met at these conferences. Yet, I can meet at least some of these people at conferences here in the Netherlands, too. Test Automation Days, the TestNet events, the Dutch Testing Day and TestMass all provide a great opportunity for me to catch up with my network. Sometimes, international conferences come to the Netherlands, too, like AutomationSTAR this year. And then there are plenty of smaller meetups here in the Netherlands (and Belgium) where I can meet and catch up with people as well. Plus, the money. I am not going to be a hypocrite and say that money doesn’t play into this. For the reasons mentioned above, I have a limited number of opportunities to travel every year, and I prefer to spend those on in-house training sessions with clients abroad, simply because the pay is much better. Even when a conference compensates flights and hotel (as they should) and offer a speaker or workshop facilitator fee (a nice bonus), it will be significantly less of a payday than when I run a training session with a client. That’s not the fault of those conferences, not at all, especially when they’re compensating their speakers fairly, but this is simply a matter of numbers and budgets. At the moment, I have one, maybe two contributions to conferences abroad coming up, and I gave them my word, so I’ll be there. That’s the SAST 30-year anniversary conference in October, plus one other conference that I’m talking to but haven’t received a ‘yes’ or ‘no’ from yet. Other than that, if conferences reach out to me, it’s likely to be a ‘no’ from now on, unless: the event pays a fee comparable to my rate for in-house training I can combine the event with paid in-house training (for example with a sponsor) it is a country or region I really, really want to visit, either for personal reasons or because I want to grow my professional network there I don’t see the first one happening soon, and the list of destinations for the third one is very short (Norway, Canada, New Zealand, that’s pretty much it), so unless we can arrange paid in-house training alongside the conference, the answer will be a ‘no’ from me. Will this reduce the number of travel opportunities for me? Maybe. Maybe not. Again, I see the number of requests I get for in-house training abroad growing, too, and if that dies down, it’ll be a sign for me that I’ll have to work harder to create those opportunities. For 2025, things are looking pretty good, with trips for training to Romania, North Macedonia and Denmark already scheduled, and several leads for more in the pipeline. And if the number of opportunities does go down, that’s fine, too. I’m happy to spend that time with family, working on other things, or riding my bike. And I’m sure there will be a few opportunities to speak at online meetups, events and webinars, too.

As is the case every year, 2025 is starting off relatively slowly. There’s not a lot of training courses to run yet, and since a few of the projects I worked on wrapped up in December, I find myself with a little bit of extra time and headspace on my hands. I actually enjoy these slower moments, because they give me some time to think about where my professional career is going, if I’m still happy with the direction it is going on, and what I would like to see changed. Last year, I quit doing full time projects as an individual contributor to development teams in favour of part-time consultancy work and more focus on my training services. 2024 has been a great year overall, and I would be happy to continue working in this way in 2025. However, as a thought experiment, I took some time to think about what it would take for me to go back to full time roles, or maybe (maybe!) even consider joining a company on a permanent basis. Please note that this post is not intended as an ‘I need a job!’ cry for help. My pipeline for 2025 is slowly but surely filling up, and again, I am very happy with the direction my career is going at the moment. However, I have learned that it never hurts to leave your options open, and even though I love the variety in my working days these days, I think I would enjoy working with one team, on one goal, for an extended amount of time, too, under the right conditions. If nothing else, this post might serve as a reference post to send to people and companies that reach out to me with a full time contract opportunity or even a permanent job opening. This is also not a list of requirements that is set in stone. As my views on what would make a great job change (and they will), I will update this post to reflect those views. So, to even consider joining a company on a full-time contract or even a permanent basis, there are basically three things I will and should consider: What does the job look like? What will I be doing on a day-to-day basis? What are the must-haves regarding terms and conditions? What are the nice to haves that would provide the icing on the cake for me? Let’s take a closer look at each of these things. What I look for in a job As I mentioned before, I am not looking for a job as an individual contributor to a development team. I have done that for many years, and it does not really give me the energy that it used to. On the other hand, I am definitely not looking for a hands-off, managerial kind of role, as I’d like to think I would make an atrocious manager. Plus, I simply enjoy being hands-on and writing code way too much to let that go. I would like to be responsible for designing and implementing the testing and automation strategy for a product I believe in. It would be a lead role, but, as mentioned, with plenty (as in daily) opportunities to get hands-on and contribute to the code. The work would have to be technically and mentally challenging enough to keep me motivated in the long term. Getting bored quickly is something I suffer from, which is the main driver behind only doing part-time projects and working on multiple different things in parallel right now. I don’t want to work for a consultancy and be ‘farmed out’ to their clients. I’ve done that pretty much my entire career, and if that’s what the job will look like, I’d rather keep working the way I’m working now. The must-haves There are (quite) a few things that are non-negotiable for me to even consider joining a company full time, no matter if it’s on a contract or a permanent basis. The pay must be excellent. Let’s not beat around the bush here: people work to make money. I do, too. I’m doing very well right now, and I don’t want that to change. The company should be output-focused, as in they don’t care when I work, how many hours I put in and where I work from, as long as the job gets done. I am sort of spoiled by my current way of working, I fully realise that, but I’ve grown to love the flexibility. By the way, please don’t read ‘flexible’ as ‘working willy-nilly’. Most work is not done in a vacuum, and you will have to coordinate with others. The key word here is ‘balance’. Collaboration should be part of the company culture. I enjoy working in pair programming and pair testing setups. What I do not like are pointless meetings, and that includes having Scrum ceremonies ‘just because’. The company should be a remote-first company. I don’t mind the occasional office day, but I value my time too much to spend hours per week on commuting. I’ve done that for years, and it is time I’ll never get back. The company should actively stimulate me contributing to conferences and meetups. Public speaking is an important part of my career at the moment, and I get a lot of value from it. I don’t want to give that up. There should be plenty of opportunities for teaching others. This is what I do for a living right now, I really enjoy it, and I’d like to think I’m pretty good at it, too. Just like with the public speaking, I don’t want to give that up. This teaching can take many forms, though. Running workshops and regular pairing with others are just two examples. The job should scratch my travel itch. I travel abroad for work on average about 5-6 times per year these days, and I would like to keep doing that, as I get a lot of energy from seeing different places and meeting people. Please note that ‘traveling’ and ‘commuting’ are two completely different things. Yes, I realize this is quite a long list, but I really enjoy my career at the moment, and there are a lot of aspects to it that I’m not ready to give up. The nice to haves There are also some things that are not strictly necessary, but would be very nice to have in a job or full time contract: The opportunity to continue working on side gigs. I have a few returning customers that I’ve been working with for years, and I would really appreciate the opportunity to continue doing that. I realise that I would have to give up some things, but there are a few clients that I would really like to keep working with. By the way, this is only a nice to have for permanent jobs. For contracting gigs, it is a must-have. It would be very nice if the technology stack that the company is using is based on C#. I’ve been doing quite a bit of work in this stack over the years and I would like to go even deeper. If the travel itch I mentioned under the must-haves could be scratched with regular travel to Canada, Norway or South Africa, three of my favourite destinations in the world, that would be a very big plus. I realize that the list of requirements above is a long one. I don’t think there is a single job out there that ticks all the boxes. But, again, I really like what I’m doing at the moment, and most of the boxes are ticked at the moment. I would absolutely consider going full time with a client or even an employer, but I want it to be a step forward, not a step back. After all, this is mostly a thought experiment at the moment, and until that perfect contract or job comes along, I’ll happily continue what I’m doing right now.