Saturday, September 30, 2017

How to integration test ASP.NET Core services, including Startup and dependency injection

After 3 years, I feel I have something valuable to share.

I have recently started to work with ASP.NET Core and even though it's a thousand times easier to test than ASP.NET MVC, thanks to its built-in Dependency Injection (IServiceCollection, IServiceProvider) and the very great TestServer, I could not find a well rounded pattern to easily test all aspects of an application, mocking at different levels and using the powerful fact that everything comes from the IServiceProvider by design.

This is very much work in progress so please, if you happen to come across this page, get in touch with any alternatives you have found or any improvements you think can be applied.

Maintaining my style, let's get on with some code. It's worth more than a thousand words.

This is what I consider the ideal integration/acceptance/end-to-end test:

public async Task WhenXThenY(
IRepository<SomeEntity> repository, // For this to work, a TestServer must have been started and
// this IRepository must be the same instance that the Controller is going to use when processing the request
WebApiClient client, // This must be wrapping an HttpClient connected to the TestServer
ISomeExternalServiceGateway gateway // Must also be the same instance to be used by the Controller)
var entityInRequiredState = CreateEntityInStateX();
await client.Post($"controller/action/{entityInRequiredState.Id}");

There are a few things to notice here:

  1. Somehow, a TestServer must be started using as much of the production configuration as possible. Obviously, we still need to be able to mock what we want.
  2. The WebApliClient must send its requests to the TestServer.
  3. The IRepository must be the same that is going to be used by the Controller when processing the request, otherwise our setup is useless.
  4. We need to use a framework that lets you decorate your tests to customize the way the parameters are injected. I'm currently using AutoFixture.

The key to make this work is to use the IServiceProvider used by the server as the source for all the instances you want to configure to setup your test. Turns out this is not trivial to achieve without doing some research and understanding some ASP.NET Core secrets, which is why I think this is a valuable thing to share.

The typical code to start an ASP.NET Core web server is:

The trick to get access to the IServiceProvider created by the WebHostBuilder, and the reason I'm sharing all this, is to provide an instance of IStartup instead of the type:

With the above in place, we can now use AutoFixture to create an instance of TestServer, keep a reference to the IServiceProvider and use it to obtain instances to be injected into the test:

  1. The attribute, to instruct AutoFixture how to resolve all parameters of the test method.
  2. The AutoFixture ICustomization that creates a fixture for the TestServer and configures a SpecimenBuilder to delegate all requests to the IServiceProvider.
Apologies for not embedding the code here but Blogger refuses to accept any of the solutions I have found to embed code. I do dislike Blogger a lot but I haven't had the time and energy required to find something else.

I will probably turn all the above into a little NuGet package. In the meantime, the gist contains all you need to get it working:

Friday, May 9, 2014

Risk, acceptance tests, why unit tests are not enough, and what can you do about it

It's time to release again (hopefully after only 1-2 weeks after your previous release) and you must answer the question: how confident are you that the software is going to do what it's supposed to do?

It's ultimately the Product Owner's decision if you should release or not, but in order to make the decision she must answer that very same question. Based on what? What information can we give her to help her support her decision?

Most teams go about it like this:
Hey, all unit tests and integration tests are passing and we have a 98% test coverage! We've manually checked that the software satisfies the acceptance criteria for the new stories we played, and we also did some manual regression testing. Everything seems to be OK. We're happy to release.
For a team to state they're happy to release when this is all the information they can provide is an act of faith in their skills. They're assuming that because unit tests are passing then the software is going to work as expected.

Unfortunately we've all been trained to fully believe in our unit tests and how good we are: surely if we test the individual methods and then the interactions by faking dependencies, we can imply that everything works, right?

Well, I'd argue there are a lot of assumptions and untested implications in the proposition "the system works because we have good unit tests coverage and those tests are passing". See my previous post about the value of unit tests, and by all means, do your Googling... the subject's been heating up recently.

Long story short, you may have all the unit tests in the world, 100% code coverage (whatever that means), and still have no certainty that the software is going to work as the developers intented. More importantly, because unit tests verify that software does what the developers wanted, you'll have even less certainty that the software is going to do what the Product Owner wanted!

Here's a good exercise you can do to get an idea of the implications you do in this process: take a couple of user stories you have already delivered and released, and try to make a map of the unit tests that guarantee that user story works as expected.

Take 1 minute and think about how would you go about it right now...

The first sign of alert should be that you had never thought about this, which is usually the case.

In most cases only imagining the exercise should be enough, but if you go ahead and are actually able to do it then you should end up with either the realization that you have blind spots (particularly around interactions) or in the best case, a big mess of tests scathered all around the code with no clear relation to a particular acceptance test.

If your Product Owner is not very technical then deciding to release after been given the former assessment on the quality of the release is an act of faith in the team. One most of us has been part of. If the Product Owner happens to be a techy then she's probably into the unit tests "religion" and is as convinced as everyone else that you can release with very high (and false) certainty things are to work as expected.

OK, you got me thinking. What can I do?

What if you could provide the following assessment on the quality:
Hey, all unit tests are passing, all the end-to-end automated acceptance tests which run in a production-like environment are passing. We've done some manual exploratory testing and didn't find any issues.
The automated acceptance tests cover 83% of all the acceptance tests, 98% of those considered critical and 95% of the new acceptance tests we've just implemented.
We're happy to release.
If you've followed your process correctly then acceptance tests represent all your Product Owner cares about. If you can tell the Product Owner 83% of the acceptance tests have been verified in a production-like environment you're basically telling her that at least 83% of the features are known to work (the only risk being how different from production the test environment is). And she can now make an informed decision of the type "no, I really need X and Y to be verified" or "great, let's go ahead".

But isn't the end-to-end automation of acceptance tests expensive?

Yes, it is. It will consume time you could spend doing something else, like implementing new features. But assuming your software is of a reasonable complexity it should very quickly be impossible to manually verify each acceptance test which is why I included risk in the title.

It's all about managing risk. If the Product Owner and the team are happy to live with the risk of regressions of bad behaviour then it makes sense to cut down on this automation, or apply it only to critical areas. In most cases this is not the case though, and the only reason releases are approved is because there's no clear picture of what the certainty is.

Here's another exercise (more of a challenge really): next time you have to release, create a list of all the acceptance tests in the stories you have already delivered and released. Then try to explain to your Product Owner how many of those have been validated for this release. Feel free to do all the magic and hand waving you want, just stay honest.

You can say "this acceptance test is covered because we have this and this and this unit tests, you see...", and "this other was tested manually and because it uses most of the same components as acceptance test X then we consider X has also been validated". This other might also work: "we haven't touched this component for a long time and because users haven't complained so far we can safely assume it's working properly".

See how much confidence can you get from your Product Owner for that release.

If your application is in any way critical to your company by this point you'll probably have a very pallid face in front of you. Clear exceptions might be some start-ups, experiments, prototypes, etc.

After perhaps a bit of hatred and arguing, and after pointing out that it's unfeasible to verify every single acceptance test before each release, this would be the time to propose that you invest in the automation of your acceptance tests, in a production-like environment.

Note that all this is very related to BDD, which has been around for a long time, but most people associate BDD with a framework and it also implies that you write your tests first, which is not the point I'm trying to make here.

Any hints on automating the acceptance tests?

Actually, yes, I have a couple of things we've been trying and I haven't seen anywhere else like having a unique set of tests that can be run fast, without any I/O, and also in a full-deployed environment.

Being able to run those tests fast give the developers a very quick feedback on their changes, much like unit tests do, especially if you use a tool like NCrunch.

The full-deployed version will be much slower so it should probably run as part of your continuos integration, but will give you much more confidence in return.

I'll try to post more details about this approach soon, but whatever you do, please start being objective about the quality of the software you're releasing. If you decide to take the step and start to automate your acceptance tests systematically then make sure you invest in quality: you'll need to maintain this code together with your production code..

Friday, March 21, 2014

Are unit tests waste?

If you're interested in how to get real confidence out of your investment in testing, see Risk, acceptance tests, why unit tests are not enough, and what can you do about it

A co-worker sent me this article from James O Coplien a few days ago:
If you get past the title (which you should), and don’t take everything it says as “the truth”, there are a lot of interesting things we could take from it. This is my personal resume from the article but I encourage everyone to read it.
You can apply many of these personally, other would require team agreement and others would even require changes to wider policies:
People confuse automated tests with unit tests: so much so that when I criticise unit testing, people rebuke me for critising automation.
Keep this in mind whilst reading the article (or this resume). This is not about removing automated tests, is about the value of testing one method in isolation (unit) versus testing at the system or sub-system level.

(...) don’t forget the Product Owner perspective in Scrum or the business analyst or Program Manager: risk management is squarely in the center of their job, which may be why Jeff Sutherland says that the PO should conceive (and at best design) the system tests as an input to, or during, Sprint Planning (...) Software engineering research has shown that the most cost-effective places to remove bugs are during the transition from analysis and design, in design itself, and in the disciplines of coding. It’s much easier to avoid putting bugs in that to take them out (…) one of my favourite cynical quotes is, “I find that weeks of coding and testing can save me hours of planning.” (...) “There’s something really sloppy about this ‘fail fast’ culture in that it encourages throwing a bunch of pasta at the wall without thinking much… in part due to an over-confidence in the level of risk mitigation that unit tests are achieving”.
This is said in many other places but you can never say it enough. Translated into process: take your time in the design meetings, don’t rush it and think it through! Do your best to get it right the first time. Don’t leave it to “the QA process” to find your errors later.
(...) you can model any program as a Turing tape, and what the program can do is somehow related to the number of bits on that tape at the start of execution. If you want to thoroughly test that program, you need a test with at least the same amount of information: i.e., another Turing tape of at least the same number of bits (…) to do complete testing, the number of lines of code in unit tests would have to be orders of magnitude larger than those in the unit under test (...) Few developers admit that they do only random or partial testing and many will tell you that they do complete testing for some assumed vision of complete. Such visions include notions such as: "Every line of code has been reached," which, from the perspective of theory of computation, is pure nonsense in terms of knowing whether the code does what it should. Unit tests are unlikely to test more than one trillionth of the functionality of any given method in a reasonable testing cycle. Get over it. (Trillion is not used rhetorically here, but is based on the different possible states given that the average object size is four words, and the conservative estimate that you are using 16-bit words).
These are some of the reasons why we absolutely need automated Acceptance Tests. It also links to the fact that we shouldn’t care about “impossible” scenarios: if something can’t happen in production then we don’t need to test it, which in turn links back to minimizing configuration options because each option increases the testing effort exponentially.
The purpose of testing is to create information about your program. (Testing does not increase quality; programming and design do. Testing just provides the insights that the team lacked to do a correct design and implementation.)
Never, ever, lose sight of this.
The third tests to throw away are the tautological ones. I see more of these than you can imagine — particularly in shops following what they call test-driven development (...) However, as with most unit tests, it’s better to make this an assertion than to pepper your test framework with such checks (...) When I look at most unit tests (...) they are assertions in disguise. When I write a great piece of software I sprinkle it with assertions that describe promises that I expect the callers of my functions to live up to, as well as promises that function makes to its clients. Those assertions evolve in the same artefact as the rest of my code (...) Turn unit tests into assertions. Use them to feed your fault-tolerance architecture on high-availability systems. This solves the problem of maintaining a lot of extra software modules that assess execution and check for correct behavior; that’s one half of a unit test. The other half is the driver that executes the code: count on your stress tests, integration tests, and system tests to do that.
This is what Code Contracts should be doing for us. Unfortunately Code Contracts seems to be taking too long to become a finished product but if you choose to get rid of it then you should at least replace the contracts with Debug.Assert.
(...) one question to ask about every test is: If this test fails, what business requirement is compromised? Most of the time, the answer is, "I don't know." If you don't know the value of the test, then the test theoretically could have zero business value. The test does have a cost: maintenance, computing time, administration, and so forth. That means the test could have net negative value.
Make sure you link your automated acceptance tests back to the original acceptance test which in turn should be linked to a requirement (User Story, Use Case, etc). If you're using some BDD framework then you might have the option to consider the automated tests as your actual acceptance tests.
If you cannot tell how a unit test failure contributes to product risk, you should evaluate whether to throw the test away. There are better techniques to attack quality lapses in the absence of formal correctness criteria, such as exploratory testing and Monte Carlo techniques. (Those are great and I view them as being in a category separate from what I am addressing here.) Don’t use unit tests for such validation.
Again, Acceptance vs Unit Tests. They aren’t the same and Acceptance Tests that link directly to requirements provide much more value.
Most programmers believe that source line coverage, or at least branch coverage, is enough. No. From the perspective of computing theory, worst-case coverage means investigating every possible combination of machine language sequences, ensuring that each instruction is reached, and proving that you have reproduced every possible configuration of bits of data in the program at every value of the program counter. (It is insufficient to reproduce the state space for just the module or class containing the function or method under test: generally, any change anywhere can show up anywhere else in a program and requires that the entire program can be retested. Long fragment but very interesting. This is why we need to minimize the number of interactions in a system.
Even if “in general” his explanation seems correct, a good design can (and should) mitigate this by applying encapsulation, SRP, cohesion, preferring immutable state when possible, etc. Make each module in the system be a black-box API to other modules, and define the interaction with well-defined contracts.
(...) The classes he was testing are code. The tests are code. Developers write code. When developers write code they insert about three system-affecting bugs per thousand lines of code. If we randomly seed my client’s code base — which includes the tests — with such bugs, we find that the tests will hold the code to an incorrect result more often than a genuine bug will cause the code to fail! Interesting point.
The numbers are clear but I believe he’s not considering that tests should be much simpler than “production code”, so the bug ratio must be much lower (the number of bugs is not a linear function of the complexity but exponential or similar).
Create system tests with good feature coverage (not code coverage) — remembering that proper response to bad inputs or other unanticipated conditions is part of your feature set.
No comments. Just do it.
In summary (from the article itself, not my words. Bold means I consider it controversial, the rest I consider we should be doing it):
  1. Keep regression tests around for up to a year — but most of those will be system-level tests rather than unit tests.
  2. Keep unit tests that test key algorithms for which there is a broad, formal, independent oracle of correctness, and for which there is ascribable business value.
  3. Except for the preceding case, if X has business value and you can test X with either a system test or a unit test, use a system test — context is everything. I understand he’s using “unit tests” referring to the scope (1 method). Speed is a different concern here.
  4. Design a test with more care than you design the code.
  5. Turn most unit tests into assertions.
  6. Throw away tests that haven’t failed in a year.
  7. Testing can’t replace good development: a high test failure rate suggests you should shorten development intervals, perhaps radically, and make sure your architecture and design regimens have teeth.
  8. If you find that individual functions being tested are trivial, double-check the way you incentivize developers’ performance. Rewarding coverage or other meaningless metrics can lead to rapid architecture decay.
  9. Be humble about what tests can achieve. Tests don’t improve quality: developers do.

Tuesday, April 16, 2013

NuGet.Server + IIS 7.5: nuget push returns 404 error with large packages

After installing a NuGet server using the NuGet.Server package I was getting 404 error when trying to push packages:

F:\test>NuGet.exe push MyPackage. -Source http://nugetrepo/ -ApiKey myApiKey

Pushing MyPackage to 'http://nugetrepo:81/'...

Failed to process request. 'Not Found'.
The remote server returned an error: (404) Not Found..

Short version

The cause in my case was that the package was too big. If your package is moderately large you need to set the maxAllowedContentLength setting to a larger number:

                <requestLimits maxAllowedContentLength="32212254720"> </requestLimits>

This setting controls the biggest file size accepted by IIS. Notice this setting is specified in bytes.

You also need to set ASP.NET's maxRequestLength setting to a corresponding large number (this time in Kb):

    <httpRuntime maxRequestLength="31457280" targetFramework="4.5"></httpRuntime>

Full version

Obvious things discarded (wrong api key, wrong URL, server not available, etc) I then turned to Fiddler. 2 requests are made by the NuGet.exe client:
  • The first one a GET to the site root (http://nugetrepo). This is sucessful.
  • A subsequent PUT to http://nugetrepo/api/v2/package which fails with a 404 error.
I went on and enabled IIS Failed Request Tracing (see here) which gave me the key piece of information: the error was a 404.13. For some reason I didn't see that 404.13 on Fiddler.

Once I knew the cause it was fairly straight forward to find the solution.

Hope this helps! It will certainly help myself in the future.

Monday, March 11, 2013

TEAM.BabyHost: leave your baby playing in the PC


If you ever wanted to leave your baby or toddler playing some game in the computer without fearing he will inadvertently (sometimes I doubt it!) do nasty things, like closing all your other windows, open every possible  application and discovering all kind of keyboard shorcuts you had never imagined existed:

TEAM.BabyHost is your friend

TEAM.BabyHost lets you open any web page in a controlled sandbox. With so many flash games already available you just need to navigate to the web page or point it to a local flash file.

Get your copy here in bitbucket.

How does it work?

TEAM.BabyHost is a full screen application which intercepts most of the special keyboard shortcuts available in Windows applications. In fact, it can intercept all shortcuts except for Ctrl+Alt+del and Windows+L. Those might be coming in the future though so if you like the application stay tuned.

As a full-screen application it prevents babies from using the mouse outside of the window too!

How does it look?


Your feedback is very welcome. Get in touch by sending an email to, by leaving a comment here or by creating an issue in bitbucket.

Single Action Controller: more improvements

It's been more than a year since the last entry and I've done more improvements to the implementation of Single Action Controller in TEAM.Commons.Web. Most of the improvements have been around removing magic strings and using types instead.

The following gist shows some examples of what you get:

If you like type safety and finding errors at compile time rather than build time, you're going to love this approach, together with enabling view compilation.

On top of that I've also added some methods to help with testing of applications built with this library. This is how you verify that an action returns a View:

And this is how you check that an action returns a redirect to another Single Action Controller:

Sunday, January 29, 2012

Single Action Controller - Take 2

After almost a year of using the first version of Single Action Controllers over the ASP.NET MVC (, I have applied a few improvements on it. I particularly didn't like the requirement to inherit from a custom class (SingleActionController), and the boilerplate code required in your Global.asax.

So, the current implementation (also available as a NuGet package at doesn't require your controller class to inherit from SingleActionController but from the usual Controller class, and provides a helper method for Autofac users:


protected void Application_Start()
  var builder = new ContainerBuilder();

  // Register your dependencies

  builder.RegisterTypesForSingleActionControllers(Assembly.GetExecutingAssembly(), "Base namespace of your controllers");

A controller:

using MyCompany.MyProject.ViewModels.Author;

// Name your namespace after your controller.
// This works very nicely with the directory structure you create in your project.
namespace MyCompany.MyProject.Controllers.Author
  // Name your class after your Action and make it inherit from the standard Controller
  public class Index : Controller
    // One single action named Execute
    public ActionResult Execute(FilterDataModel filter) { ... }