ArgumentDisplayFormatter is being ignored in 0.77.3

[Brokolis]

A custom ArgumentDisplayFormatter is being ignored. Here's a minimal reproduction with a failing test because of it (here's a repo with the repro):

public class Tests
{
    [Test]
    [MethodDataSource(nameof(Data1))]
    [ArgumentDisplayFormatter<FooFormatter>]
    public void Test1(Foo foo)
    {
    }

    public IEnumerable<Foo> Data1() => [new()];
}

public class Foo
{
    public override string ToString() => throw new Exception("Foo.ToString");
}

public class FooFormatter : ArgumentDisplayFormatter
{
    public override bool CanHandle(object? value) => true;

    public override string FormatValue(object? value) => "FooFormatterValue";
}

The test fails because the FooFormatter isn't being used and the Foo.ToString() method gets called and throws:

PS D:\Projects\others\TUnitBugs> dotnet test
Restore complete (0.4s)
  TUnitBugs succeeded (0.2s) → TUnitBugs\bin\Debug\net9.0\TUnitBugs.dll
  TUnitBugs test failed with 2 error(s) (0.4s)
    D:\\Projects\\others\\TUnitBugs\\TUnitBugs\\Tests.cs(3): error test failed: 
      Test1 (0ms): InvalidOperationException: Failed to expand data source for test 'Test1': Foo.ToString
      
    D:\Projects\others\TUnitBugs\TUnitBugs\bin\Debug\net9.0\TUnitBugs.dll : error run failed: Tests failed: 'D:\Projects\others\TUnitBugs\TUnitBugs\bin\Debug\net9.0\TestResults\TUnitBugs_net9.0_x64.log' [net9.0|x64]

Test summary: total: 1, failed: 1, succeeded: 0, skipped: 0, duration: 0.3s
Build failed with 2 error(s) in 1.1s

I found that this happens because the argument display value is computed before the formatter is added.

The argument display value is being created here:

TUnit/TUnit.Engine/Building/TestBuilder.cs

Lines 771 to 783 in 6ed6416

	// Create the test object BEFORE invoking event receivers
	// This ensures context.InternalExecutableTest is set for error handling in registration
	var creationContext = new ExecutableTestCreationContext
	{
	TestId = testId,
	DisplayName = context.GetDisplayName(),
	Arguments = testData.MethodData,
	ClassArguments = testData.ClassData,
	Context = context,
	TestClassInstanceFactory = testData.TestClassInstanceFactory,
	ResolvedMethodGenericArguments = testData.ResolvedMethodGenericArguments,
	ResolvedClassGenericArguments = testData.ResolvedClassGenericArguments
	};

Which happens before the events are executed for the test later:

TUnit/TUnit.Engine/Building/TestBuilder.cs

Line 803 in 6ed6416

await InvokeDiscoveryEventReceiversAsync(context);

And ArgumentDisplayFormatterAttribute depends on having it's OnTestDiscovered executed so it could add the argument formatter.

I discovered this, because I have a class that throws for the default argument formatter, so I'm using a custom one to make sure my tests don't fail. Except right now the tests are failing anyways.

[Brokolis]

The formatter value is being used after the fix, but if .ToString or .GetEnumerator throws for the data value, the test will still fail and not run. Not sure if you want to change that, but you might at least want to fix the added ArgumentDisplayFormatterTests, since they currently fail and as such don't even check anything.

[Brokolis]

I see you fixed it in #3566, thanks, you're the best! 😃