Lesson 3 - Java Testing - Hamcrest, JUnit TestRule and Best Practices

In the previous lesson, Java Testing - The first unit test in JUnit, we introduced the very basics of JUnit and wrote our first unit test. In today's lesson, we're going to complete unit tests by introducing the Hamcrest library, which is newly supported by JUnit, and fundamentally changes the way we write assertions. We'll also discuss rules (TestRules) and at the end we'll mention best practices for writing unit tests.

Hamcrest matchers

Since JUnit 4.4, there's the assertThat() method available, bringing a new way to do asserts using Matchers from the Hamcrest library. By combining these matchers, we can create a complex expression easily. You may not be surprised that matchers are classes (again) with static methods, we can chain them and we're also able to write custom matchers. Using this new method results in great readability.

Let's see what one simple assertion would look like in the original syntax:

assertEquals(2, calculator.add(1, 1));

and now in Hamcrest:

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