Collections.HaveElementAt object is doing reference equals and not checking for IEquatable

Description

(Collections).HaveElementAt is using System.Object.Equals for equality check, and not checking for IEquatable and invoking that if available. Maybe there’s a more appropriate method?

Complete minimal example reproducing the issue

[Test]
public void MyLibrary_Testing()
{
  // Arrange
  var testobj = new TestObject { Index = 0 };
  var testobjCollection = new TestObject[] { testobj };

  // Act
  var result = testobjCollection;

  // Assert
  result.Should().HaveElementAt(0, new TestObj { Index=0 }); //this doesnt work
  result.Should().HaveElementAt(0, testobjCollection[0]); //this works since references are equal
}
public class TestObject : IEquatable<TestObject>
{
  public int Index { get;set; }
  public bool Equals(TestObject other)
  {
    if(other==null) return false;
    if(this.Index != other.Index) return false;
    return true;
  }
}

Expected behavior:

HaveElementAt looks at collection index 0, checks equality by invoking IEquatable since interface was present on TestObject.

Actual behavior:

Output from test:

Message: Expected 

RESTQueryTests.QueryableExtensions_AddPaging_Tests+TestObject
{
   Index = 0
} at index 0, but found 

RESTQueryTests.QueryableExtensions_AddPaging_Tests+TestObject
{
   Index = 0
}.

Clearly basically the same object from IEquatable standpoint, but two different objects from ReferenceEquals standpoint.

Versions

• Which version of Fluent Assertions are you using? 5.4.1
• Which .NET runtime and version are you targeting? Net Framework 4.5.2

[dennisdoomen]

From the MSDN docs on IEquatable(T).

If you implement IEquatable<T>, you should also override the base class implementations of Object.Equals(Object) and GetHashCode so that their behavior is consistent with that of the IEquatable<T>.Equals method.

[ericnewton76]

Yes, just figured that out when I added override Equals to TestObj:

https://github.com/ericnewton76/RESTQuery/commit/b562191fe28e0712df3f65d5d9f4d5c0bccdc756

Sorry. Kinda Net 101 mistake right there. Maybe I’ll send a PR for some of the method summaries to remind of that.