Question

How do I assert in MSTest that the order of the returned collection is correct?

[TestMethod]
    public void when_sorting_movies_it_should_be_able_to_sort_all_movies_by_title_descending()
    {
        populateTestMovies(movie_collection);
        MovieLibrary movieLibrary = new MovieLibrary(movie_collection);
        IEnumerable<Movie> results = movieLibrary.sort_all_movies_by_title_descending();
        Assert.IsTrue(results.Contains(theres_something_about_mary));
        Assert.IsTrue(results.Contains(the_ring));
        Assert.IsTrue(results.Contains(shrek));
        Assert.IsTrue(results.Contains(pirates_of_the_carribean));
        Assert.IsTrue(results.Contains(indiana_jones_and_the_temple_of_doom));
        Assert.IsTrue(results.Contains(cars));
        Assert.IsTrue(results.Contains(a_bugs_life));
        Assert.AreEqual(7, results.Count());
    }

Answer 1

Create a hard-coded IEnumerable<string> with the movie titles in the expected order, pull the titles from the result collection and use SequenceEqual to check that they come in the same order (assuming your referred constants are Movie objects, and that Movie has a Title property):

IEnumerable<string> expected = new[] 
{ 
    theres_something_about_mary.Title, 
    the_ring.Title,
   /* and so on */ 
};
Assert.IsTrue(results.Select(m => m.Title).SequenceEqual(expected));