Tag Archives: TestCase

NUnit TestCaseSource

While working on this project, I found a need to abstract away a base type that the unit tests use (in this instance, it was a queue type). I was only testing a single type (PriorityQueue); however, I wanted to create a new type, but all the basic tests for the new type are the same as the existing ones. This led me to investigate the TestCaseSource attribute in NUnit.

As a result, I needed a way to re-use the tests. There are definitely multiple ways to do this; the simplest one is probably to create a factory class, and pass in a string parameter. The only thing that put me off this is that you end up with the following test case:

        [TestCase("test", "test9", "test", "test2", "test3", "test4", "test5", "test6", "test7", "test8", "test9"]
        [TestCase("a1", "a", "a1", "b", "c", "d", "a"]
        public void Queue_Dequeue_CheckResultOrdering(
            string first, string last, params string[] queueItems)
        {

Becoming:

        [TestCase("PriorityQueue", "test", "test9", "test", "test2", "test3", "test4", "test5", "test6", "test7", "test8", "test9"]
        [TestCase("PriorityQueue2", "test", "test9", "test", "test2", "test3", "test4", "test5", "test6", "test7", "test8", "test9"]
        [TestCase("PriorityQueue", "a1", "a", "a1", "b", "c", "d", "a"]
        [TestCase("PriorityQueue2", "a1", "a", "a1", "b", "c", "d", "a"]
        public void Queue_Dequeue_CheckResultOrdering(
            string queueType, string first, string last, params string[] queueItems)
        {

This isn’t very scaleable when adding a third or fourth type.

TestCaseSource

It turns out that the (or an least an) answer to this is to use NUnit’s TestCaseSource attribute. The NUnit code base dog foods quite extensively, so that is not a bad place to look for examples of how this works; however, what I couldn’t find was a way to mix and match. To better illustrate the point; here’s the first test that I changed to use TestCaseSource:

        [Test]
        public void Queue_NoEntries_CheckCount()
        {
            // Arrange
            PQueue.PriorityQueue<string> queue = new PQueue.PriorityQueue<string>();

            // Act
            int count = queue.Count();

            // Assert
            Assert.AreEqual(0, count);
        }

Which became:

        [Test, TestCaseSource(typeof(TestableQueueItemFactory), "ReturnQueueTypes")]
        public void Queue_NoEntries_CheckCount(IQueue<string> queue)
        {
            // Arrange


            // Act
            int count = queue.Count();

            // Assert
            Assert.AreEqual(0, count);
        }

(For completeness, the TestableQueueItemFactory is here):

    public static class TestableQueueItemFactory
    {
        public static IEnumerable<IQueue<string>> ReturnQueueTypes()
        {
            yield return new PQueue.PriorityQueue<string>();
        }
    }

However, when you have a TestCase like the one above, there’s a need for the equivalent of this (which doesn’t work):

        [Test, TestCaseSource(typeof(TestableQueueItemFactory), "ReturnQueueTypes")]
        [TestCase("test", "test9", "test", "test2", "test3", "test4", "test5", "test6", "test7", "test8", "test9")]
        [TestCase("a1", "a", "a1", "b", "c", "d", "a")]
        public void Queue_Dequeue_CheckResultOrdering(string first, string last, params string[] queueItems)
        {

A quick look at the NUnit code base reveals these attributes to be mutually exclusive.

Compromise

By no means is this a perfect solution, but the one that I settled on was to create a second TestCaseSource helper method, which looks like this (along with the test):

        private static IEnumerable Queue_Dequeue_CheckResultOrdering_TestCase()
        {
            foreach(var queueType in TestableQueueItemFactory.ReturnQueueTypes())
            {
                yield return new object[] { queueType, "test", "test9", new string[] { "test", "test2", "test3", "test4", "test5", "test6", "test7", "test8", "test9" } };
                yield return new object[] { queueType, "a1", "a", new string[] { "a1", "b", "c", "d", "a" } };
            }
        }

        [Test, TestCaseSource("Queue_Dequeue_CheckResultOrdering_TestCase")]
        public void Queue_Dequeue_CheckResultOrdering(
            IQueue <string> queue, string first, string last, params string[] queueItems)
        {

As you can see, the second helper method doesn’t really help readability, so it’s certainly not a perfect solution; in fact, with a single queue type, this makes the code more complex and less readable. However, When a second and third queue type are introduced, the test suddenly becomes resilient.

YAGNI

At first glance, this may appear to be an example of YAGNI. However, in this article, Martin Fowler does state:

Yagni only applies to capabilities built into the software to support a presumptive feature, it does not apply to effort to make the software easier to modify.

Which, I believe, is what we are doing here.

References

http://www.smaclellan.com/posts/parameterized-tests-made-simple/

http://stackoverflow.com/questions/16346903/how-to-use-multiple-testcasesource-attributes-for-an-n-unit-test

https://github.com/nunit/docs/wiki/TestCaseSource-Attribute

http://dotnetgeek.tumblr.com/post/2851360238/exploiting-nunit-attributes-valuesourceattribute

https://github.com/nunit/docs/wiki/TestCaseSource-Attribute

Using MSTest DataRow as a Substitute for NUnit TestCase

I used to believe that Nunit’s TestCase test (that is, an ability to define a test and then simply pass it alternate parameters) was denied MSTest users. It appears that this is, at least now, fallacious.

The following article implies that this is a recent change:

Taking the MSTest Framework forward with “MSTest V2”

This particular example is in a UWP application:

        [DataTestMethod]
        [DataRow(1, 2, 3, 6)]
        [DataRow(8, 2, 3, 13)]
        [DataRow(8, 5, 3, 12)]
        public void AddNumbers(int num1, int num2, int num3, int total)
        {
            Assert.AreEqual(num1 + num2 + num3, total);
        }

Will result in a failing test, and:

        [DataTestMethod]
        [DataRow(1, 2, 3, 6)]
        [DataRow(8, 2, 3, 13)]
        [DataRow(8, 5, 3, 16)]
        public void AddNumbers(int num1, int num2, int num3, int total)
        {
            Assert.AreEqual(num1 + num2 + num3, total);
        }

Results in a passing one.

If you want additional information relating to the test, you can use this syntax:

        [DataTestMethod]
        [DataRow(1, 2, 3, 6, DisplayName = "First test")]
        [DataRow(8, 2, 3, 13, DisplayName = "Second test")]
        [DataRow(8, 5, 3, 15, DisplayName = "This will fail")]
        public void AddNumbers(int num1, int num2, int num3, int total)
        {
            Assert.AreEqual(num1 + num2 + num3, total);
        }

Given the constant problems that I have with finding the correct NUnit test adaptor, and trying to work out which are the right libraries, I think, despite coming late to this party, MS might actually drag people back to MSTest with this.

Unit Tests Are Not Discoverable

I recently had a situation where I loaded a solution containing a suite of NUnit tests, but the test explorer would not recognise them. The following is a series of checks to make that may cause unit tests to be not visible. Most of these are applicable to all tests:

1. Tests must be declared as public. For example:

        public void MyTestMethod()
        {

2. Tests must be decorated with a test attribute.

For NUnit this is is [Test]:

	        [Test]
	        public void MyNUnitTest()
	        {
	

Or [TestCase]:

	        [TestCase(1)]
	        [TestCase(2)]
	        public void MyParameterisedTest(int testNum)
	        {
	
	

For MSTest this is [TestMethod]:

	        [TestMethod]
	        public void MyTestMethod()
	        {
	

3. If using NUnit – check that the correct version is installed (remember that v3 is not an official release yet – that is, at the time of writing).

The current release test adapter is here

The test adaptor for NUnit3 is here

As usual, this is more for my own reference, but if it helps anyone else then all to the good. Also, if you think of or encounter another then please let me know in the comments and I’ll add it on.