C# – Use Assert.ThrowsException instead of ExpectedException attribute

If you’re using the built-in MSTest unit testing framework, you may be used to the old way of asserting exceptions by using the [ExpectedException] attribute. The following example illustrates one of the key problems with this approach: The ArgumentNullException is being thrown, so the test passes. However, the exception is being thrown in the arrange … Read more

C# – How to unit test code that uses HttpClient

HttpClient is a dependency. Like any other dependency, you need to pass it into your code (aka dependency injection). By passing it in, you can mock it out in unit tests. There are two approaches to mocking it out: Wrap the HttpClient and mock out the wrapper. Use a real HttpClient with a mocked out … Read more

C# – Parameterized tests with MSTest v2

Here’s an example of how to parameterize your tests using the built-in MSTest v2 test framework: There are 3 steps: Add parameters to your test method. Use [DataTestMethod] instead of [TestMethod]. For each test case, add [DataRow(…)] to pass in the parameters for that test case. What parameters can you pass in? You pass in … Read more

C# – How to unit test async methods

Let’s say you have the following async method you want to test: Here’s how to unit test this: This is awaiting the method you’re testing. To await it, you must make the unit test method return async Task. This example is a bit simplistic. In the real world when you are working with async methods, … Read more

How to mock static methods

The need to mock static methods in order to add a unit test is a very common problem. It’s often the case that these static methods are in third-party libraries. There are many utility libraries that are completely made up of static methods. While this makes them very easy to use, it makes them really … Read more