JUnit cheatsheet

A one-page reference for JUnit 5. For the extension model and interview Q&A, see the complete guide.

📖 Full guide: JUnit →

Core annotations

@Test
void addsNumbers() { assertEquals(4, 2 + 2); }

@BeforeEach void setup() { ... }
@AfterEach  void teardown() { ... }
@BeforeAll static void once() { ... }
@Disabled("flaky, see JIRA-123")

Assertions & assumptions

assertEquals(expected, actual);
assertThrows(IllegalArgumentException.class, () -> parse(""));
assertAll(
  () -> assertTrue(user.isActive()),
  () -> assertEquals("Bob", user.getName())
);
assumeTrue(isCI());   // skip test if false, doesn't fail

Parameterized tests

@ParameterizedTest
@ValueSource(strings = {"", " ", "\t"})
void blankStrings(String input) {
    assertTrue(input.isBlank());
}

@ParameterizedTest
@CsvSource({"1,1,2", "2,3,5"})
void add(int a, int b, int sum) {
    assertEquals(sum, a + b);
}

@Nested tests

class UserTest {
  @Nested class WhenActive {
    @Test void canLogin() { ... }
  }
  @Nested class WhenSuspended {
    @Test void cannotLogin() { ... }
  }
}

Groups related scenarios, readable failure output by context.

Tagging & filtering

@Tag("smoke")
class LoginTest { ... }

mvn test -Dgroups="smoke"

Extension model

@ExtendWith(MockitoExtension.class)
class ServiceTest {
    @Mock Repository repo;
}

Replaces JUnit 4 @RunWith — composable, multiple extensions per class.

Parallel execution

# junit-platform.properties
junit.jupiter.execution.parallel.enabled=true
junit.jupiter.execution.parallel.mode.default=concurrent

JUnit 5 vs TestNG

	JUnit 5	TestNG
Parameterized	@ParameterizedTest	@DataProvider
Grouping	@Tag	@Groups
Parallel	config-based	native, more granular

See: JUnit 5 vs. TestNG