Exercise 3: Write Assertions for a Map

After you have finished this exercise, you understand how you can write assertions for maps by using Hamcrest. Let’s start by taking a look at the system under test.

The TagRepository interface declares one method (findCountByTagName()) that returns a map which describes how many times each tag has been used. If no tags is found from the database, this method returns an empty map.

For example, this method could return a map that has two key-value mappings:

The source code of the TagRepository interface looks as follows:

import java.util.Map;

interface TagRepository {

    Map<String, Integer> findCountByTagName();
}

The TagService class has one method called findCountByTagName() which simply invokes the findCountByTagName() method of the TagRepository interface and returns the map that’s returned by the invoked method.

The source code of the TagService class looks as follows:

import java.util.Map;

public class TagService {

    private final TagRepository repository;

    public TagService(TagRepository repository) {
        this.repository = repository;
    }

    public Map<String, Integer> findCountByTagName() {
        return repository.findCountByTagName();
    }
}

During this exercise you will write unit tests for the findCountByTagName() method of the TagService class. You can finish this exercise by following these steps:

1. Open the TagServiceTest class that’s found from the com.cleantestautomation.junit5intro.tag package.

2. Write the assertion which verifies that the system under test is working as expected when no tags is found from the database. You can find the relevant test method from this nested test class: FindCountByTagName -> WhenNoTagsIsFound. Remember to use Hamcrest.

3. Write the assertions which ensure that the system under test is working as expected when two tags are found from the database. You can find the relevant test methods from this nested test class: FindCountByTagName -> WhenTwoTagsAreFound. Remember to use Hamcrest.

4. Run the tests found from the TagServiceTest class and make sure that they pass.