AutoFixture VS FsCheck

Yes, it does feel like some of the "standard stuff" in other more nuanced languages are missing (especially miss AutoFixture ngl). Some of those are a conscious decison by the golang team for example.

Our first test is very easy, I like to name my tests as MethodName_GivenCondition_ShouldExpectedResult to follow the pattern, I have added GetById_GivenRecordDoesNotExist_ShouldReturnNull and I am going to leavarage excellent AutoFixture to get a new Guid as parameter. For this test we don't need arrange part, we would skip to the act and then assert. For Assertion I am going to use FluentAssertions. For this test we need to assert the returned result is null.

The next test to talk about, is that if this was a bank, we would have multiple customers, who can hold multiple accounts that we need to calculate the interest for. You could manually construct these objects if you want, but I'm going to use a package called AutoFixture to make life easier.

AutoFixture is an amazing library that simplifies the process of creating test data in .NET. If for some reason you don't use this fantastic tool, it's time to consider it. Today, I'm going to share some tips for using AutoFixture that will be beneficial for developers of all skill levels. Let's get started!

AutoFixture

Ensuring that your test is still readable and not bloated by the setup of those variables may be quite a challenge but hopefully no more with AutoFixture, let's see how!

One neat library for creating and generating test data is AutoFixture.  The creators describe it as follows:

First time I heard of Bogus, looks interesting, been using AutoFixture for those will definitely take a look at it.

As you can see from the imports statement we're relying on FsCheck to generate some random values for us.

C# - FsCheck

https://fscheck.github.io/FsCheck/ can hopefully generate random inputs automatically or with low effort for many methods to get your code coverage up. You don’t even need to write real tests right now, just call the methods with the random inputs and check they don’t fail.

Try using F# for tests. It has some great libraries like FsCheck (https://fscheck.github.io/FsCheck/).

At Symbolica we're building a symbolic execution service that explores every reachable state of a user's program and verifies assertions at each of these states to check that the program is correct. By default it will check for common undefined behaviours, such as out-of-bounds memory reads or divide by zero, but it can also be used with custom, application specific, assertions too just like the kind you'd write in a unit test. Seen from this perspective it's kind of like FsCheck (or Haskell's QuickCheck or Python's Hypothesis), but much more exhaustive and without the randomness.

Maybe something like QuickCheck, a quick search gave me this library for .NET https://github.com/fscheck/FsCheck

Because of the above I've generally been using tools like Stryker.NET and FsCheck to augment my testing suite. I'm still doing unit testing to find the more obvious "I haven't had my coffee, let's make sure I'm doing what I think I'm doing" bugs. I'm just using things like mutation testing, property testing, fuzzing, etc. to find the deeper issues in my code. There's a ton of libraries out there, including one that I've built for myself to help with testing but FsCheck and Stryker are just beautiful. And if you're interested in fuzzing, SharpFuzz is a great option. But that one isn't quite as easy of an on ramp compared to the other two that I mentioned.

Looks cool. Is there a reason why you didn't use FsCheck or Hedgehog? They're built to generate random data for testing, and can return the seed if a test fails so you can rerun the test with the exact same data once you figure out what the problem is - which is useful if the failure condition is rare.

Haskell has QuickCheck and Hedgehog, and dotnet has both as well. F# is favored, but there's C# interop.

Side note, if you are thinking about testing in general, might be interested in property based testing. See for example https://fscheck.github.io/FsCheck/