Assert.Equal for sets and a custom Func comparer throws NotImplementedException

[AndriySvyryd]

[Fact]
public void Test()
{
    Assert.Equal(new HashSet<int> { 1 }, new HashSet<int> { 1 }, AreEqual);

    static bool AreEqual(int x, int y) => true;
}

throws

Message: 
System.NotImplementedException : The method or operation is not implemented.
Stack Trace: 
HashSet1.AddIfNotPresent(T value, Int32& location) HashSet1.UnionWith(IEnumerable1 other) HashSet1.ctor(IEnumerable1 collection, IEqualityComparer1 comparer)
RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
MethodBaseInvoker.InvokeDirectByRefWithFewArgs(Object obj, Span`1 copyOfArgs, BindingFlags invokeAttr)

Surprisingly, this doesn't throw:

[Fact]
public void Test()
{
    Assert.Equal(new HashSet<int> { 1 }, new HashSet<int> { 1 }, (x, y) => true);
}

V2.5.3

[bradwilson]

Available in v2: 2.5.4-pre.7
Available in v3: 0.1.1-pre.301