How to compare IReadOnlyCollection to List for equality by value?

Question

I am trying to write a unit test to compare actual results to expected results, where the class I am testing gives me a IReadOnlyCollection and my expected results are List.

I read over the this answer about comparing Lists using CollectionAssert at How to compare Lists in Unit Testing, however when I attempt to do so, I get compiler error "cannot convert from 'System.Collections.Generic.IReadOnlyCollection' to 'System.Collections.ICollection'"

Here is my test method:

    [TestMethod]
    public void EveningMotion()
    {
        IDateTimeProvider dateTimeProvider = new MockDateTimeProvider(new DateTime(2018, 1, 1, 20, 0, 0));
        ILightHardwareInterface frontyardLights = new MockLightHardwareInterface();
        MockLightHardwareInterface backyardLights = new MockLightHardwareInterface();

        LightController controller = new LightController(dateTimeProvider, frontyardLights, backyardLights);
        controller.ActuateLights(true);

        IReadOnlyCollection<bool> actualResult = backyardLights.GetRecording();
        List<bool> expectedResult = new List<bool>
        {
            true
        };

        CollectionAssert.AreEqual(expectedResult, actualResult);
    }

What is one to do? I kind of want to keep the expected and actual results comparison rather than iterating through both element by element, if possible.

Are you using a specific Assertion library or is that just the default one that MS uses? Also, Core or what framework version? — Matti Price, Jan 02 '18 at 22:40
@matti Just the built in unit test stuff. Framework 4.5 on VS 2015. — Christopher Pisz, Jan 02 '18 at 22:41
Even if they were both `List` that approach will not work. Loop through and compare them or better yet do what icepickle has suggested above. — CodingYoshi, Jan 02 '18 at 22:42
Assert that length of your constructed list == lenght of readonly collection + assert IsTrue for `ReadOnly.Single() == List.Single()` — Patrick Artner, Jan 02 '18 at 22:46
That's doing a reference comparison, try [`CollectionAssert.AreEqual`](https://msdn.microsoft.com/en-us/library/ms243736.aspx?f=255&MSPPError=-2147217396) — juharr, Jan 02 '18 at 22:46
@juharr " cannot convert from IReadOnlyCollection to System.Collections.ICollection " — Christopher Pisz, Jan 02 '18 at 23:10
@SirRufo ToList method does not exist on IReadOnlyCollection — Christopher Pisz, Jan 02 '18 at 23:18
@ChristopherPisz Computer says: "It does." https://msdn.microsoft.com/library/hh881542(v=vs.110).aspx — Sir Rufo, Jan 02 '18 at 23:20
@ChristopherPisz Try `new List(actualResult)` instead or add `using System.Linq` — juharr, Jan 02 '18 at 23:20
The [second highest voted answer](https://stackoverflow.com/a/11055746/3744182) from the linked question should work fine. — dbc, Jan 02 '18 at 23:40

score 1 · Accepted Answer · answered Jan 02 '18 at 22:46

1

You can use CollectionAssert for collections.

CollectionAssert.AreEqual(expectedResult, actualResult);

answered Jan 02 '18 at 22:46

Django

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cannot convert from IReadOnlyCollection to System.Collections.ICollection – Christopher Pisz Jan 02 '18 at 23:07
1

What is the concrete type of IReadOnlyCollection result? If it is System.Collections.ObjectModel.ReadOnlyCollection, you can cast it to ICollection. – Django Jan 02 '18 at 23:27
Problem solved doing it that way. Side question, Is casting via CollectionAssert.AreEqual(expectedResult, (ICollection)actualResult); type safe? I thought it was akin to a reinterpret cast in C++ (I am still a C# noob) and that there would be an "as" method if it was safe. – Christopher Pisz Jan 03 '18 at 16:42

How to compare IReadOnlyCollection to List for equality by value?

1 Answers1