Assert that a large enumerable contains only the very same item n times?

[drauch]

I have a collection of 100K sample numbers. In one test case I want to assert that all of them are of the same value. I tried:

values.Should().AllBeEquivalentTo(5);

This takes quite some time (around five seconds). Which is WAY to long. Is this a bug in the implementation? Why is it taking so long? I think it's the wrong function, but I couldn't find a .AllBe(5) for which I was looking for originally.

My workaround now is values.Distinct().Should().BeEquivalentTo(new[]{5}); but I don't like it because it doesn't express my intent.

Ideas on how to do that properly?

[dennisdoomen]

It's a performance bug. The current implementation is using a very naive approach.

[krajek]

@dennisdoomen Are you going to fix it or can I jump in?

[dennisdoomen]

By all means, jump in

[krajek]

@drauch I have just tried to reproduce the problem with following test.

[Fact] public void When_some_subject_items_are_not_equivalent_to_expectation_for_huge_table_execution_time_should_still_be_short()
{
    //-----------------------------------------------------------------------------------------------------------
    // Arrange
    //-----------------------------------------------------------------------------------------------------------
    const int N = 1000000;
    var subject = new List<int>(N) {1};
    for (int i = 1; i < N; i++)
    {
        subject.Add(2);
    }

    //-----------------------------------------------------------------------------------------------------------
    // Act
    //-----------------------------------------------------------------------------------------------------------
    Action action = () =>
    {
        try { subject.Should().AllBeEquivalentTo(1); }
        catch (Exception)
        {
            // ignored, we only care about execution time
        }
    };

    ////-----------------------------------------------------------------------------------------------------------
    //// Assert
    ////-----------------------------------------------------------------------------------------------------------
    action.ExecutionTime().Should().BeLessThan(150.Milliseconds());
}

On my machine it always passes, even for more elements than 100K. Could you provide minimal, complete and verifiable example?

[krajek]

@drauch Forget my last comment, I was looking at the wrong test after all. I confirm that execution time gets excessively long for larger collections.

[drauch]

Thanks!

[drauch]

Are you going to release this soon? :)

[jnyrup]

Yes, we're fixing up the last things to get 5.5.0 ready.
https://github.com/fluentassertions/fluentassertions/milestone/12

So stay tuned, we're also eager to get out a new release.