Assert.Equal failing for value-slot collections of different concrete types

[FlorianHockmann]

One of our tests starts failing in version 2.6.2 and 2.6.3, but it still worked in 2.6.1 (and versions before that).
The test compares two collections which contain a Dictionary that contains collections as its values. One of these nested collections is an object[] whereas the other is a List<object>.

This is a minimal example to reproduce the problem:

var expected = new List<object> { new Dictionary<object, object> { { 1, new List<object> { 2 } } } };
var actual = new object[] { new Dictionary<object, object> { { 1, new object[] { 2 } } } };

Assert.Equal(expected, actual);

It fails with:

Assert.Equal() Failure: Exception thrown during comparison
                        ↓ (pos 0)
Expected: List<object> [[[1] = [2]]]
Actual:   object[]     [[[1] = [2]]]
                        ↑ (pos 0)

System.InvalidCastException
Unable to cast object of type 'System.Object[]' to type 'System.Collections.Generic.List`1[System.Object]'.

The InvalidCastException comes from the nested collection in the Dictionary, not the outer collection.

[bradwilson]

Bummer. That means the fix for #2821 broke this. Not sure what the fix is yet.

Edit: I've determined what this is, fix is incoming.

[bradwilson]

This also affects both keys and values for comparing KeyValuePair<K,V>.

[bradwilson]

Available in v2: 2.6.4-pre.5
Available in v3: 0.1.1-pre.334

https://xunit.net/docs/using-ci-builds

[FlorianHockmann]

Thanks a lot for the really fast response and fix! 😃