OrderedMerge missing unit tests

[atifaziz]

OrderedMerge is completely missing unit tests.

[c9952594]

I'd like to take this.

[atifaziz]

@c9952594 Thanks for stepping forward and offering to help with this. Looking forward to your PR.

[c9952594]

@atifaziz While adding tests I think I may have found a bug. The code below shows the current behaviour.

I would expect that first and second would be ordered before the merge is performed, see OrderedMerge.cs below.

Is the current behaviour correct? If not then I can fix this at the same time.

OrderedMergeTest.cs

[Test]
public void ShowHowItWorks()
{
    var pickedPreferentially = new Version("1.0");
    var first = new[] { pickedPreferentially, new Version("3.0"), new Version("2.0"), new Version("5.0") };

    var discardedPreferentially = new Version("1.0");
    var second = new[] { discardedPreferentially, new Version("4.0"), new Version("3.0"), new Version("2.0") };

    var merged = first.OrderedMerge(second).ToArray();

    var expected = new[] {
        new Version("1.0"),                     // Compare (First)1 and (Second)1
        new Version("3.0"), new Version("2.0"), // Take (First)3 and (First)2 because less than (Second)4
        new Version("4.0"), new Version("5.0"), // Compare (First)5 and (Second)4
        new Version("3.0"), new Version("2.0")  // Take remaining (Second)3 and (Second)2
    };
        
    Assert.That(merged, Is.EquivalentTo(expected));
    Assert.That(merged.First(), Is.SameAs(pickedPreferentially));

    //var shouldBe = new[] { new Version("1.0"), new Version("2.0"), new Version("3.0"), new Version("4.0"), new Version("5.0") };
    //Assert.That(merged, Is.EquivalentTo(shouldBe));
    //Assert.That(merged.First(), Is.SameAs(pickedPreferentially));
}

OrderedMerge.cs

289: using (var e1 = first.OrderBy(firstKeySelector).GetEnumerator())
290: using (var e2 = second.OrderBy(secondKeySelector).GetEnumerator())

[atifaziz]

I think I may have found a bug.

Generally, it's best to open a separate issue for that, even if you're looking for confirmation that it's potentially a bug.

If not then I can fix this at the same time.

Again, this would be best done as a separate PR. I wouldn't fix it at the same time.

That all said, the documentation says:

Merges two ordered sequences into one. Where the elements equal in both sequences, the element from the first sequence is returned in the resulting sequence.

The key here is ordered sequences. first and second from your example are not ordered so the behaviour is undefined.