Assert.Empty（msgs）和Assert.False（msgs.Any（））有什么区别？

Question

I am using XUnit to test for scenarios where an empty Enumerable list is expected.

I have noticed that in certain scenarios:

• Assert.Empty(msgs); fails;

BUT

• Assert.False(msgs.Any()); is passing.

This is a bit confusing to me as I anticipated that this was testing for the same thing.

I understand that this likely because of the differences in expected behaviour between:

1. Enumerable.Any() (which defines this as "Determines whether a sequence contains any elements.")

AND

2. The empty expected in XUnit.Empty() (which defines that this is testing for an empty Object).

However, I am not sure exactly the difference as it appeared to me to be essentially testing the same thing.

Could someone please explain the differences in what is being tested for in these two different types of Asserts?

Answer 1

Here is the source for Enumerable.Any (The Assert.False() just validates that this returns false .):

public static bool Any<TSource>(this IEnumerable<TSource> source) {
    if (source == null) throw Error.ArgumentNull("source");
    using (IEnumerator<TSource> e = source.GetEnumerator()) {
        if (e.MoveNext()) return true;
    }
    return false;
}

Here is the source for Assert.Empty from xUnit:

public static void Empty(IEnumerable collection)
{
    Assert.GuardArgumentNotNull("collection", collection);

    var enumerator = collection.GetEnumerator();
    try
    {
        if (enumerator.MoveNext())
            throw new EmptyException(collection);
    }
    finally
    {
        (enumerator as IDisposable)?.Dispose();
    }
}

They seem to be using a very similar way of checking for the presence of items in the collection. I'd expect the same result from each method.

Without more details about how you are using each one, it's hard to say why you are getting different results.

Answer 2

msge.Any() returns true when msge is not null and have one or more element and false otherwise so probebly msge is null and Assert.Empty fails when argument is null.
With the best regards.

Answer 3

There is a difference between these two methods:

.Any() is an extension method which takes an IEnumerable - An object an implement the IEnumerable interface to let the code iterate through it for set operations, (like .Any() or .Where())

Assert.Empty() doesn't appear to check whether an object implements IEnumerable, but only checks against an empty set if the input data is a string or an array.

My guess then is that you're passing in an IEnumerable object, rather than an array.

To get around this you could either use Assert.False(msgs.Any()); as before, or else use something like Assert.Empty(msgs.ToArray());