Message when asserting null with Is.EquivalentTo could be more helpful

[appel1]

If result.Things is null in the following example the failure message is a little bit confusing.

Assert.That(result.Things, Is.EquivalentTo(new[] { "abc" }));

Message:
System.ArgumentException : The actual value must be an IEnumerable

Perhaps the null case could have a more specific message?

[ChrisMaddock]

I don't see any harm in someone implementing this. I think it may be slightly non-trivial, but I haven't looked in detail.

As I'm sure you're aware, if result.Things is possibly null, for now you could do:

Assert.That(result.Things, Is.Not.Null.And.EquivalentTo(new[] { "abc" }));

[ChrisMaddock]

I'll label this up-for-grabs soon, but would like to give it 24 hours or so, and give anyone else the chance to disagree!

[mikkelbu]

I also think that this is a reasonable wish.

Note, that "the change" probably needs to be done in approx 10 places to be consistent, as we have similar checks for IEnumerable in most collection constraints.

[ChrisMaddock]

I was overthinking this.

It would be trivial to include a different error message when actual is null. The current error message is meant for when a non-ienumerable is passed in, not when a 'null ienumerable' is passed in. It would be more involved to instead produce a custom failure message.

[jnm2]

I'm not opposed to changing it to a failure message like Expected: IEnumerable But was: null.

But if we keep it as an exception message, I've always thought it was the perfect message. It's a well-known C# fact that null is not IEnumerable (see null is IEnumerable).