Integration tests verify that several parts of an app work together correctly and give us more confidence than unit tests in terms of ensuring that the app as a whole is working as expected. These tests provide the most scope in terms of what is tested because of the many app part combinations that we can choose to test.

These tests are generally quick to execute because slow components such as database and network requests are often mocked out. The time it takes to write and maintain these tests is also short.

For single-page applications, the return on investment (ROI) of integration tests is arguably greater than the other two testing types if we choose our tests wisely. This is why the relevant box in the preceding diagram is bigger than other testing types.

Now that we understand the different types of test, we are going to start implementing them on our Q and A app. We'll start by unit-testing the .NET backend.