Test with Expecto

[Entomy]

Upon looking better into unit testing frameworks due to numerous frustrations, I found Expecto addresses numerous of the concerns I've had. Of particular note is integration of performance testing into the unit testing. It's incredibly tedious to maintain these separately. Furthermore, because this is an F# library, and we're developing in C# primarily with F# binding, testing through Expecto automatically tests the entire through-binding call-chain.

There are a few pitfalls but I'm not overly concerned with it.

1. Contributors need to have a basic understanding of F# and a less common testing framework. In practice this shouldn't be a problem. One, there's barely any contributors. And two, this doesn't involve advanced F# features. This actually includes the benefit of forcing F# bindings to be provided, which is great, and indirectly recompletes this older issue.
2. Testing is done through the F# bindings, which includes the binding overhead. On one hand this penalty is important to gather. On the other hand, it's includes performance details that potentially make for unfair comparisons for C#/VB consumers. This is easy to work around through standard benchmarking. Since Expecto still uses BenchmarkDotNet this means the same benchmark runner can be used in both cases, which greatly assists data analysis.
3. There are situations where F# calls do not go through the same path as C# calls, or the F# call is otherwise different from the C# call. An example is slicing, where C# uses a this[Range] call and F# uses a very different GetSlice(start, finish) call. While internally these both uses Slice(start, length) there's a degree of marshalling in both cases, and testing strictly through F# will not test the C# marshalling side. This issue still exists now, just in the opposite direction, as testing exclusively through C# avoids the F# binding and marshalling code. Both tests still need to be done, I'm just encouraging F# first.

[Entomy]

Okay... this is a problem. I can qualify functions as needed, but it's hard to deny that the resulting tests become ugly as fuck.

[Entomy]

I'm not going through with this. For various reasons, I've needed to write my own testing framework, and anything Expecto could have offered is something I can easily implement as well.

[Entomy]

I'm happy with the new approach and can add benchmarking components into it.