4. Unit Tests

  • At the end of the objects review topic the implementation was played with

  • This allowed testing the basic functionality

  • However, the testing was far from through or systematic

4.1. Unit Testing

  • Ideally, when testing code, each unit or component should be tested

    • Unit Testing

    • Ideally with good coverage

  • When doing so, individual test methods are written to test the units/components

  • These tests can also be run automatically

  • By writing tests like this, it adds intentionality to the code and tests

    • Take the time to think of the cases needing testing

    • It can also help keep the units/components isolated

  • It also obviously helps with testing and debugging

  • It there are ever breaking changes to the unit/component being tested, the automated testing should find it

  • Writing tests can be a bit of an art, so it’s best to get a lot of practice

4.2. JUnit

  • JUnit is a very popular unit testing framework for Java

  • It’s simple to use and automates testing

  • Within IntelliJ, there is a simple way to setup JUnit

  1. Make a new folder/directory called test in the project next to src

    ../../_images/test_folder.png

    Right click the project in the project view and select New -> Directory. Call this new directory “test”.

  2. Right click the test folder and select Mark Directory as -> Test Sources Root

    ../../_images/mark_tests.png

    Right click the new “test” folder to mark it as the “Test Sources Root”.

  3. Create a new class for testing named such that it is the class name followed by “Test”

    • For example, FriendTest

  4. Add JUnit to the class path

    • A simple way to do it is to write @Test in the new class and press Alt + Enter

  5. Select Add ‘JUnit5…

    • Do not select Junit 4… as that will cause issues with the tests

    ../../_images/alt_enter.png

    Pressing Alt + Enter with @Test selected will cause a popup to appear where “Junit5…” will be an option. Alternatively, one could select the dropdown arrow on the red light bulb for the same menu.

4.3. Testing the Friend Class

  • Checkout the FriendTest.java for testing the Friend class

  • For now, the new ideas introduced here are

    • @Test annotation — marking a method as a test

    • Assertions — a mechanism for checking something

  • Below are excerpts from the FriendTest class

10    @Test
11    void getFirstName_generalCase_returnsFirstName() {
12        Friend friend = new Friend("qwerty", "asdfgh", "zxcvbn");
13        assertEquals("qwerty", friend.getFirstName());
14    }

  • Consider the first test within the test class as shown above

  • The method is marked with @Test to mark the method as a test method for Junit

  • It has a descriptive name of the form unitUnderTest_case_expectedResult

    • getFirstName_generalCase_returnsFirstName

    • getFirstName is the method being tested

    • Since there is no real special condition or case for this test, it has generalCase in its name

    • returnsFirstName is the expected result of calling the method

  • It uses assertEquals to check that the expected string "qwerty" is what is returned by getFirstName()

30    @Test
31    void equals_equalFriendObjects_areEqual() {
32        Friend aFriend = new Friend("qwerty", "asdfgh", "zxcvbn");
33        Friend bFriend = new Friend("qwerty", "asdfgh", "zxcvbn");
34        assertEquals(aFriend, bFriend);
35    }

  • Consider the above two tests

    • equals_equalFriendObjects_areEqual

    • equals_unequalFriendObjects_areNotEqual

  • These tests are named such that the cases (equal/unequal Friend objects) is clear

  • These tests also make use of different asserts

    • assertEquals

    • assertNotEquals

Warning

The above tests for equality are sufficient for the purposes of this course, but they could be improved. Within the provided FriendTest class is a test method that makes use of EqualsVerifier, which helps with testing equality on objects. Although this improved equality test is provided, the simpler equality tests are fine here. Do note that EqualsVerifier is an external dependency that is not included with Java or IntelliJ.

52    @Test
53    void equals_verify_contract() {
54        EqualsVerifier.forClass(Friend.class)
55                .withNonnullFields("firstName")
56                .withNonnullFields("lastName")
57                .withNonnullFields("email")
58                .verify();
59    }

4.4. For Next Time

  • Read Chapter 1 of the text

    • 15 pages

4.4.1. Playing Code