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SameValuesAsAssertion calls Enumerable.GetEnumerator twice


I noticed some unexpected behaviour of SameValuesAsAssertion.

Consider the following test:

var sue = new SingleUseEnumerable<int>(new int[] {});
sue.Should().Have.SameValuesAs(new int[]{});


class SingleUseEnumerable<T> : IEnumerable<T>
    private readonly IEnumerable<T> _component;
    private bool _used;

    public SingleUseEnumerable(IEnumerable<T> component)
        _component = component;

    public IEnumerator<T> GetEnumerator()
        if (_used)
            throw new InvalidOperationException("Enumerator can only be retrieved once.");
        _used = true;
        return _component.GetEnumerator();

    IEnumerator IEnumerable.GetEnumerator()
        return GetEnumerator();
This test always throws an InvalidOperationException, because SameValuesAsAssertion calls Enumerable.GetEnumerator twice.
From my point of view, I would not expect this behaviour.

A possible fix would be to rewrite line 20 of SameValuesAsAssertion to this:

a = a.ToArray(); // only call GetEnumerator once!
return !a.Except(expected).Concat(expected.Except(a)).Any();
Closed Sep 25, 2011 at 3:01 PM by fabiomaulo
Fixed thanks for the test