new Analyzer+CodeFix: recommend against wrong assertion method (e.g. Assert.IsTrue(x != null))

[LukasGelke]

Summary

As some assertions may be written in different ways, some of them provide a better experience: better/richer message, clearer intent, better readability/maintainability.

Background and Motivation

• default Exception-Messages are better

string text = "Mouse";
Assert.IsTrue("House" == text);
//  Assert.IsTrue failed.
Assert.AreEqual("House", text);
// Assert.AreEqual failed. Expected:<House>. Actual:<Mouse>. 

This is also useful when a test is failing in a pipeline, or you get the stack trace only. This way you may not have to dig too deep and "waste" time debugging, just to get to that point to know what text actually is. Or when you get a notification from the pipeline a la test method "VeryImportantTest" failed with message "Assert.IsTrue failed."

• we have a company-internal analyzer that does this.
• xUnit has a similar analyzers:
  • https://xunit.net/xunit.analyzers/rules/xUnit2003
  • https://xunit.net/xunit.analyzers/rules/xUnit2004
• (though for some tests, it is explicitly wanted due to explicit testing of operator overload; but for those case the warning is just disabled via #pragma or Attribute)

Proposed Feature

essentially all permutations of IsFalse/IsTrue with is/is not/==/!=

• Assert.IsNotNull, e.g.

  • Assert.IsTrue(x != null) => Assert.IsNotNull(x)
  • Assert.IsTrue(null != x) => Assert.IsNotNull(x)
  • Assert.IsFalse(x != null) => Assert.IsNull(x)
  • Assert.IsTrue(x is not null) => Assert.IsNotNull(x)
  • ...
  • Assert.AreNotEqual(null, x) => Assert.IsNotNull(x)
  • ...
  • either side may be null literal

• Assert.Are[Not]Equal, e.g.

  • Assert.IsTrue(x == y) => Assert.AreEqual(x, y)
  • Assert.IsTrue(x != y) => Assert.AreNotEqual(x, y)
  • Assert.IsFalse(x == y) => Assert.AreNotEqual(x, y)
  • Assert.IsFalse(x != y) => Assert.AreEqual(x, y)
  • ...
  • maybe don't be overly smart, and just let the 'const in expected' be handled by the other analyzer

• Assert.IsTrue/IsFalse, e.g.

  • Assert.AreEqual(true, b) => Assert.IsTrue(b)
  • only when there is a bool const as one param
  • may be a cascaded result result from Assert.IsTrue(true == b), stupid, but possible; again, just let it do one step at a time, for simplicity?

Edit 1:
maybe also consider:

• Assert.AreEqual(typeof(string), o.GetType()) => Assert.IsInstanceOfType<string>(o)

also wouldn't matter to me if they are all the same DiagnosticID, since those cases are all "wrong similarly"

Alternative Designs

As mentioned, our analyzer grew over time and is quite complex. And I'm not sure if we have a bug or a missing case. Having such an Analyzer+CodeFix in MsTest directly would also provide a wider audience for finding such "bugs".

AB#2200926

[LukasGelke]

Even though it's more tedious than complex, I was given permission to share our existing code for this Analyzer and CodeFix if necessary, since it only affects MsTest.
I may also be able to contribute it directly, if I could get the build to work. However due to current planning, this is only possible on 2014-08-26 at the earliest. (and as per guide, would only start if this is approved and I'm allowed to do so)

[Evangelink]

Hi @LukasGelke,

I have a good idea of how to implement this analyzer but if you are allowed to share the code, please feel free to paste it/enclose it here. If we haven't yet started by end of August, please feel free to do the contribution :)

Thanks again!

[LukasGelke]

Hey @Evangelink, I'm sorry. But i just got around to start working on this.
All seems good, except one thing: .\Build.cmd and VS (.\MSTest.slnf) still complain that net5 is somehow missing.
Also the dev pack for net5 is not available for VS2022, so I'm not sure what to install, except the "plain" SDK.
The docs/dev-guide.md seems a bit out-of-date since Universal Windows Platform development and .Net Core cross-platform development are available as "workloads" anymore(?). I do however have the "individual component" Windows 10 SDK (10.0.20348.0) installed already. (My machine is still Win10)

I've successfully install net9 (from the "plain" installer) though; as complained at me by the global.json which now seems to work.

C:\Program Files\Microsoft Visual Studio\2022\Enterprise\MSBuild\Current\Bin\Microsoft.Common.CurrentVersion.targets(12
59,5): error MSB3644: The reference assemblies for .NETCore,Version=v5.0 were not found. To resolve this, install the D
eveloper Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Frame
work Developer Packs at https://aka.ms/msbuild/developerpacks [D:\GitHub\testfx\src\Adapter\MSTestAdapter.PlatformServi
ces\MSTestAdapter.PlatformServices.csproj::TargetFramework=uap10.0.16299]
C:\Program Files\Microsoft Visual Studio\2022\Enterprise\MSBuild\Current\Bin\Microsoft.Common.CurrentVersion.targets(12
59,5): error MSB3644: The reference assemblies for .NETCore,Version=v5.0 were not found. To resolve this, install the D
eveloper Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Frame
work Developer Packs at https://aka.ms/msbuild/developerpacks [D:\GitHub\testfx\src\Adapter\MSTest.TestAdapter\MSTest.T
estAdapter.csproj::TargetFramework=uap10.0.16299]
C:\Program Files\Microsoft Visual Studio\2022\Enterprise\MSBuild\Current\Bin\Microsoft.Common.CurrentVersion.targets(12
59,5): error MSB3644: The reference assemblies for .NETCore,Version=v5.0 were not found. To resolve this, install the D
eveloper Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Frame
work Developer Packs at https://aka.ms/msbuild/developerpacks [D:\GitHub\testfx\src\TestFramework\TestFramework.Extensi
ons\TestFramework.Extensions.csproj::TargetFramework=uap10.0.16299]

> dotnet --list-sdks
5.0.408 [C:\Program Files\dotnet\sdk]
6.0.425 [C:\Program Files\dotnet\sdk]
7.0.102 [C:\Program Files\dotnet\sdk]
7.0.120 [C:\Program Files\dotnet\sdk]
8.0.108 [C:\Program Files\dotnet\sdk]
8.0.206 [C:\Program Files\dotnet\sdk]
8.0.400 [C:\Program Files\dotnet\sdk]
9.0.100-rc.1.24452.12 [C:\Program Files\dotnet\sdk]

> dotnet --list-runtimes
Microsoft.AspNetCore.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.33 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 7.0.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 8.0.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 8.0.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 9.0.0-rc.1.24452.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.33 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.2 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 9.0.0-rc.1.24431.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.33 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 7.0.2 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 8.0.6 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 8.0.8 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 9.0.0-rc.1.24452.1 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

[Youssef1313]

Assert.AreEqual(typeof(string), o.GetType()) may be different from IsInstanceOfType in certain cases. This is because IsInstanceOfType doesn't check for the exact type, but uses IsAssignableFrom. For example, IsInstanceOfType<object> will always pass, but Assert.AreEqual(typeof(object), o.GetType()) may not.

[Youssef1313]

The analyzer is now implemented. The issue is open to track implementing codefix