Question

I am new to JUnit and facing difficulty in writing JUnit.

I have an interface and a class

Interface

public interface Student{

    List<String> getStudentList();
    void setStudentList(List<String> studentList);
    void createStudentList();
}

Class

public class StudentServiceImpl implements Student{

        private List<String> studentList

        public List<String> getStudentList() {
            return studentList;
        }


        public void setStudentList(final List<String> studentList){
            this.studentList = studentList;
        }

        public void createStudentList(){
            if (studentList == null) {
                studentList = new ArrayList<String>();
                studentList.add("John");
                studentList.add("Bill");
                studentList.add("Ricky");
                studentList.add("Jack");
            }
            setStudentList(studentList);
        }
    }

What is the best to write Junit for above class. What should be kept in mind while writing JUnit cases. Can somebody help me?

Answer 1

Here is an example of IMHO well-written test case (written in notepad, please correct if does not compile):

import static org.fest.assertions.Assertions.assertThat;

public class StudentTest {

    private final Student student = new StudentServiceImpl();

    @Test
    public void shouldReturnEmptyListOfStudentsWhenNotInitialized() {
        //given

        //when
        List<String> students = student.getStudentList();

        //then
        assertThat(students).isEmpty();
    }

    @Test
    public void shouldReturnSomeStudentsWhenListCreated() {
        //given
        student.createStudentList();

        //when
        List<String> students = student.getStudentList();

        //then
        assertThat(students).containsExactly("John", "Bill", "Ricky", "Jack");
    }

    @Test
    public void shouldStorePreviouslySetListOfStudents() {
        //given
        student.setStudentList(Arrays.asList("Jane", "Bob"));

        //when
        List<String> students = student.getStudentList();

        //then
        assertThat(students).containsExactly("Jane", "Bob");
    }

}

Few tips:

1. Keep tests short and simple

2. Test name should describe what use case is being tested

3. Separate setup code, tested logic and assertions

4. Code should be easy to read. Use fluent and descriptive libraries like FEST

Further improvements:

1. The first test should fail, do you know why?

2. There are still few tests missing, do you know which ones?