implemented non-generic overload for Assert.ContainsSingle

[AtolagbeMuiz]

This Pull Request fixes Assert.ContainsSingle should accept non-generic collections #6732

This Implementation involves an overload being added to the Assert.ContainsSingle which allows non-generic collections like ArrayList.

Current Behaviour

Assert.ContainsSingle throws compile time error because it only accepts generic collections.

Expected Behaviour

With this Implementation, Assert.ContainsSingle will allow non-generic collection as seen below;

[AtolagbeMuiz]

@Youssef1313 do we need to hndle AssertSingleInterpolatedStringHandler for non-generic collection as well

public static object ContainsSingle(IEnumerable collection, [InterpolatedStringHandlerArgument(nameof(collection))] ref AssertSingleInterpolatedStringHandler message, [CallerArgumentExpression(nameof(collection))] string collectionExpression = "") => message.ComputeAssertion(collectionExpression);

[AtolagbeMuiz]

removed the AssertSingleInterpolatedStringHandler for non-generic implemnation based because we didnt implement if for Assert.Count as well....

@Youssef1313

[Evangelink]

For the 2 new APIs, we could instead call the generic version by doing .Cast<object>(). There is a potential small performance hit but I think it's ok.

WDYT @Youssef1313

[Evangelink]

Reviving my earlier comment, I would personally use Cast<object> to avoid to have to maintain both implementations, the perf cost is IMO neglictible.

[Evangelink]

I'd remove this test as it has no value compared to test below (besides test comment is wrong).

[Evangelink]

Please add another test case like:

 public void ContainsSingle_InNonGenericCollection_AssertCustomMessage_WithEmptyCollection_ThrowsException()
    {
        // Arrange
        var collection = new ArrayList();

        // Act
        Action action = () => Assert.ContainsSingle(collection, "my custom message");

        // Assert
        action.Should().Throw<AssertFailedException>().WithMessage("Assert.ContainsSingle failed. Expected collection to contain exactly one element but found 0 element(s). 'collection' expression: 'collection'.");
Comment view    }

[Youssef1313]

@Evangelink I would personally avoid .Cast<object>. It might fail scenarios like:

unsafe
{
    var x = new int*[] { (int*)1 };
    IEnumerable y = x;
    Assert.ContainsSingle(y);
}

It might also be worth adding such test :)

[Youssef1313]

Actually the scenario above might be invalid either way.

[Youssef1313]

Are we creating a list unnecessary? We only care about first match and acount.

[Youssef1313]

This method can be written in terms of the predicate method, where the predicate is just static _ => true.