Testing in C#

Testing your code is a crucial practice for every developer. Automated testing ensures that your code works as expected every time it runs. Tests also function as internal documentation, giving a fellow programmer instructions on how to properly execute your classes and methods. While these purposes are the same for C# as any other language, the implementation of tests will look a bit different.

This course covers unit testing in C# with a test framework called MSTest. Unit testing is based on breaking down the codebase into its smallest building blocks, individual statements and methods, and testing those building blocks.


If you would like to review the benefits of automated testing, take a peek at this section in another LaunchCode text.

Why We Test


When we refactor code, we rewrite it without adding new features. Refactoring can increase efficiency at runtime, but it may also mean inadvertently introducing some bugs in the process. Unit tests verify the most basic functionality of your code, thus safeguarding against bugs introduced in refactoring.

Imagine this common workflow:

  1. You practice test-driven development (TDD), writing your tests to stipulate how your class’s code should behave.

  2. You write your class’s code to pass the tests.

  3. Later, a stakeholder in the project requests that you refactor your code using different syntax.

The features of the application will be the same, but the implementation of those features will change. Because the changes in implementation do not effect change in the application features, unit tests can help with refactoring the codebase. If your tests continue to pass after the refactor, you can move on, knowing you have not inadvertently introduced a bug. Writing tests just once provides innumerable benefits for the whole lifetime of the codebase.


In addition to assisting with refactoring, unit tests serve as vital documentation for fellow programmers. Again, because unit tests address the most fundamental tasks of your classes, they serve as live-code use-cases. You may also have an external documentation directory with examples of how to run your project, or perhaps you have been writing comments within your code to best communicate with your teammates about your changes. Both of these are great choices and should be done when possible. However, these choices also require more forethought to maintain. Each time you update your code, you might not remember to update the documentation and comments. With unit testing, however, you have a more obvious reminder that a change has been made if a previously-passing test fails.

Testing Best Practices

Below are some best practices to keep in mind when writing unit tests, in any language.

  1. The AAAs

    The AAAs of unit testing refers to the pattern to follow when writing your unit tests.

    1. Arrange the variables your test requires.
    2. Act on the methods your test requires.
    3. Assert the anticipated comparison of the expected and actual values.
  2. Deterministic

    Every time a test is run, it should produce the same outcome. A test that passes only most of the time is a worthless test.

  3. Relevant

    Group tests by related class and function.

  4. Meaningful

    There is no need to test trivial code. For example, unless a getter or setter contains some additional functionality, you do not need to write a test for those methods.

Check Your Understanding


True or False: Comments are the best tool to make your code readable.


Unit tests are a form of:

  1. Manual testing
  2. Automated testing
  3. Integration testing
  4. Documentation testing