[suggestion] New diagnostic: Use AllItemsConstraint for better assertion messages in case of failure

[Bartleby2718]

Today, NUnit.Analyzers (4.2.0) doesn't flag the following code:

var numbers = new[] { 1, 2, 3 };
Assert.That(numbers.All<int>(x => x % 2 == 0));

However, NUnit has a constraint to support this use case:

Assert.That(numbers, Has.All.Matches<int>(x => x % 2 == 0));

so I think NUnit.Analyzers should suggest a fix for a better error message.

Notes:

1. It appears that the type parameter is required for Matches, but I'm not sure if Roslyn will be able to deduce it if the type parameter is absent (i.e. convert Assert.That(numbers.All(x => x % 2 == 0)); to the same Assert.That(numbers, Has.All.Matches<int>(x => x % 2 == 0));).
2. There's a typo in the link (custom custom), but I'm not sure where it's source-controlled.

[Bartleby2718]

@manfred-brands I see that Is and Has are basically the same:

• https://github.com/nunit/nunit/blob/master/src/NUnitFramework/framework/Is.cs#L28-L33
• https://github.com/nunit/nunit/blob/master/src/NUnitFramework/framework/Has.cs#L27-L32

Questions

1. Is there another one that does the same?
2. Which one should we choose?