Java Testing Standards

Priority: P0 (CRITICAL)

High-reliability testing using JUnit 5 and fluent assertions.

Implementation Guidelines

• Framework: Use JUnit 5 (Jupiter). Avoid JUnit 4.
• Assertions: Use AssertJ (assertThat) over JUnit assertEquals. It's more readable and provides better error messages.
• Naming: MethodName_StateUnderTesting_ExpectedBehavior or @DisplayName("Should return X when Y").
• Parameterized: Use @ParameterizedTest with @ValueSource or @MethodSource for data-driven tests.
• Mocking: Use Mockito. Strictly limit mocking to external dependencies (I/O). Do not mock data objects.
• Integration: Use Testcontainers for real databases/brokers in integration tests (*IT.java).
• Visibility: Test classes and methods can be package-private in JUnit 5 (no public needed).

Anti-Patterns

• Logic in Tests: Tests should be declarative. No loops or heavy if/else.
• System.out: Never print in tests. Use Assertions.
• Legacy Assertions: Avoid assertTrue(a == b). Use assertThat(a).isEqualTo(b).
• Global State: Tests must be isolated. No strict dependency on execution order.

Code

For a full Mockito + AssertJ test class template: references/junit-template.md

// JUnit 5 + AssertJ
import static org.assertj.core.api.Assertions.assertThat;

class UserServiceTest {

    @Test
    @DisplayName("Should detect active users")
    void shouldDetectActiveUsers() {
        // Arrange
        var user = new User("id", "active");

        // Act
        boolean isActive = service.isActive(user);

        // Assert
        assertThat(isActive)
            .as("Check active user status")
            .isTrue();
    }
}

Related Topics

best-practices | quality-assurance