Unravel › Java concepts › Testing

At a glance

1. 1Structure each test as arrange (set up data), act (call the code), assert (check the outcome)assertEquals(expected, actual) takes the expected value first.
2. 2@BeforeEach runs before every test to give each a fresh start, so tests do not depend on each other or on order
3. 3assertThrows(IllegalArgumentException.class, () -> service.run(null)) checks that a failure happens as designed
4. 4@ParameterizedTest runs one test with many inputs, which is good for boundary values

• Test behaviour, not implementation details, and keep tests fast and independent
• JUnit 5 finds tests with a discovery engine, creates a new test class instance per method by default (which is why instance fields do not leak between tests), and reports through the platform launcher used by Maven, Gradle and IDEs

@Testvoid rejectsNegativeAmounts() {    PaymentService service = new PaymentService(new FakeGateway());    assertThrows(IllegalArgumentException.class, () -> service.pay(-5));}

1. line 1 uses Test, the core of JUnit tests
2. line 4 uses assertThrows, the core of JUnit tests

How Unravel recognises it

When you paste code, Unravel looks for these signs of junit tests. Spotting them yourself is a good habit when you read unfamiliar code:

• Annotations: @Test @BeforeEach @AfterEach @BeforeAll @AfterAll @ParameterizedTest @DisplayName @SpringBootTest @ExtendWith
• Types: Assertions
• Method calls: assertEquals() assertTrue() assertThrows() assertThat()

Part of a learning path

• Reliable code · previous: Retry and circuit breaker · next: Mockito mocks
• Testing enterprise code · next: Advanced JUnit 5 and async assertions

Related concepts

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