Comparing two arrays in unit test throwing a AssertFailedException

Question

I'm writing an unit tests for ready code and I'm receiving an unexpected AssertFailedException trying to run one of the test. Here is he:

[TestMethod]
    public void TestPositionGetter()
    {
        testPlayer.Position = new int[] { 1, 3 };
        int[] expectedPosition = testPlayer.Position;
        Assert.AreEqual(expectedPosition, testPlayer.Position);
    }

And here is the Position property in the Player class that I'm trying to test:

public int[] Position
    {
        get
        {
            return new int[] { this.PositionX, this.PositionY };
        }
        set
        {
            this.PositionX = value[0];
            this.PositionY = value[1];
        }
    }

Debugging the test, in local variables window player.Position and expectedPosition are looking similar but the test is still failing. I'm afraid the problem is coming from references.

Since there is already a good answer, I would like to suggest grabbing FluentAssertions as it has a ton of really nice methods for working with IEnumerable objects and other objects in general. — TyCobb
– TyCobb, Commented Jun 28, 2014 at 7:06

Anri · Accepted Answer · 2014-06-28 07:02:59Z

45

You are comparing different instances of an int[]. Assert.AreEqual compares by reference. Try CollectionAssert.AreEqual.

CollectionAssert.AreEqual(expectedPosition, testPlayer.Position);

This will compare array elements.

Also, your Position property smells like bad design. Do you really have to create new array every time you get a value?

answered Jun 28, 2014 at 7:02

Anri

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3 Comments

Stanimir Yakimov Over a year ago

I have no idea, I just have to write the tests. But tell me what's your idea.

Anri Over a year ago

Well, I would need to see the whole class, but from what is pasted here - you should create private int[] _position; in that class and use it in your getter and setter instead of creating new array every time.

George Birbilis Over a year ago

if you pass a private array reference to a caller as result of a property getter, they can keep the reference to it and change values in it / cause hard to find bugs

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