05. Exercise: Defining Custom Annotations

Exercise: Defining Custom Annotations

Testing with Reflection: Part 1

Your team at Udacisearch has a lot of business logic written in Java, but the test coverage is not very good!

You have identified the lack of testing as an area for improvement, and to help address the issue, you are developing a proprietary testing framework for running Java unit tests. Sure, there are plenty of existing unit testing frameworks for Java (such as JUnit), but your legal team has told you due to contractual and licensing reasons, an in-house testing solution is required.

You briefly discussed your plans with a teammate, and you already have a basic idea for how to design the testing framework:

1. Test engineers will write Java classes that contain their unit tests. These test classes will extend a base interface, UnitTest defined by the framework. UnitTest provides two abstract methods:
   • void beforeEachTest() runs before each unit test to set up the test environment; and
   • void afterEachTest() runs after each unit test to clean up the test environment
     By the way, these methods will allow test engineers to create simple test fixtures, which are a fundamental concept in unit testing.
2. Next, the test engineers will mark their "top-level" unit test methods with a @Test annotation provided by your framework. There may be other helper methods used to create test objects or assist with the test environment, but only the actual unit test methods should be annotated with @Test.
3. Finally, a TestRunner class has a main() method that decides which tests to run. It finds unit tests annotated with @Test, runs them, and reports the test results.

There is a lot to unpack here!

For starters, you will be completing the most basic piece: defining the custom @Test annotation. The other parts of the testing framework will be implemented in later exercises.

This exercise should be pretty short; the starter code already defines the UnitTest interface and a sample unit test class (remember the Calculator class from Lesson 1?). Just define the @Test annotation (in its own Java file), and make sure to give it the appropriate visibility, target element (@Target) and retention policy (@Retention) for the use cases described above. If you need a reminder about these concepts, you can go back to the previous page in this lesson.

Next, open up CalculatorTest.java and annotate the testAddition and testSubtraction methods with the new @Test annotation.

You don't really have a main() method to run yet — just make sure everything compiles when you're done:

javac *.java