Broken API to chain collection assertions

[maximerety]

Problem

The code snippet to chain collection assertions from https://tunit.dev/docs/assertions/collections#chaining-collection-assertions does not compile (tested with latest TUnit v1.5.33):

[Test]
public async Task Chained_Collection_Assertions()
{
    var numbers = new[] { 1, 2, 3, 4, 5 };

    await Assert.That(numbers)
        .IsNotEmpty()
        .And.Count().IsEqualTo(5)
        .And.Contains(3)
        .And.DoesNotContain(10)
        .And.IsInOrder()
        .And.All(n => n > 0)
        .And.Any(n => n == 5);
}

with the error:

The type 'int' cannot be used as type parameter 'TCollection' in the generic type or method 'CollectionContainsAssertionExtensions.Contains<TCollection, TItem>(IAssertionSource, TItem, IEqualityComparer?, string?, string?)'. There is no boxing conversion from 'int' to 'System.Collections.Generic.IEnumerable'.

Investigation

Possible source of the problem: #3926 (released with v1.3.0).

[thomhurst]

Pushing out a new update for this.

The one caveat is that you'll have to slightly change one of your lines. Chaining can only work based on what the last object returned was, and Count() (without an inner lambda) maps to an int, so you can't get back to the collection.

When the next version is out, this should work:

[Test]
public async Task Chained_Collection_Assertions()
{
    var numbers = new[] { 1, 2, 3, 4, 5 };

    await Assert.That(numbers)
        .IsNotEmpty()
-       .And.Count().IsEqualTo(5)
+       .And.Count(count => count.IsEqualTo(5))
        .And.Contains(3)
        .And.DoesNotContain(10)
        .And.IsInOrder()
        .And.All(n => n > 0)
        .And.Any(n => n == 5);
}

[maximerety]

Pushing out a new update for this.

The one caveat is that you'll have to slightly change one of your lines. Chaining can only work based on what the last object returned was, and Count() (without an inner lambda) maps to an int, so you can't get back to the collection.

Thanks @thomhurst.

It looks like you've be able to fix further as the original syntax is compiling and working fine now 👍

(The alternative version with the inner assertion does not though, which is expected if I understand correctly the changes from #4043).