JUnit Interview Questions for Automation Testing (1970)

JUnit is the de-facto Java unit testing framework. JUnit 5 (aka Jupiter) is the 2026 default — modular architecture, native parameterized tests, dynamic tests, and rich extension model.

Every Java-based automation stack (Selenium, REST Assured, Playwright-Java, Appium) integrates natively with a JUnit runner. JUnit provides the lifecycle, assertions, and parallel-execution plumbing so automation code stays focused on test logic.

• JUnit Platform — foundation for launching testing frameworks on the JVM
• JUnit Jupiter — the new API for writing tests (@Test, extensions)
• JUnit Vintage — backwards-compat runner for JUnit 3/4 tests

<dependency>
  <groupId>org.junit.jupiter</groupId>
  <artifactId>junit-jupiter</artifactId>
  <version>5.10.2</version>
  <scope>test</scope>
</dependency>

mvn test -Dtest=LoginTest#validCredentials
# Gradle
./gradlew test --tests LoginTest.validCredentials

• @BeforeAll / @AfterAll — once per class (static by default)
• @BeforeEach / @AfterEach — before/after every test
• @Test, @RepeatedTest, @ParameterizedTest
• @Disabled, @Tag, @Nested, @Timeout

JUnit 4 used @Before / @BeforeClass. JUnit 5 renamed them to @BeforeEach / @BeforeAll for clarity. Same semantics: per-test vs per-class-once.

Yes — annotate the class with @TestInstance(Lifecycle.PER_CLASS). Otherwise it must be static.

@Test @Tag("smoke") @Tag("regression")
void loginTest() {}

mvn test -Dgroups=smoke

class OrderTest {
  @Nested class WhenLoggedIn {
    @Test void canCheckout() {}
  }
}

Great for BDD-style grouping.

@Test @Timeout(value = 500, unit = TimeUnit.MILLISECONDS)
void mustBeFast() {}

import static org.junit.jupiter.api.Assertions.*;
assertEquals(expected, actual);
assertTrue(list.contains("qa"));
assertThrows(IllegalArgumentException.class, () -> svc.create(null));
assertAll("user",
  () -> assertEquals("Ada", user.name()),
  () -> assertTrue(user.active())
);

When you want to check multiple properties and see all failures at once instead of stopping at the first one. Similar to TestNG's soft assertions.

assumeTrue(System.getenv("CI") != null);
// Test is aborted (not failed) if the assumption is false

assertThrows passes only if the expected exception is thrown. assertDoesNotThrow passes only if no exception is thrown — used for happy-path safety nets.

@ParameterizedTest
@ValueSource(strings = {"admin@x.com", "qa@x.com"})
void isEmail(String s) { assertTrue(s.contains("@")); }

@ParameterizedTest
@CsvSource({ "1,2,3", "5,7,12" })
void add(int a, int b, int expected) {
  assertEquals(expected, a + b);
}

static Stream<Arguments> logins() {
  return Stream.of(arguments("a@x.com","p"), arguments("b@x.com","q"));
}
@ParameterizedTest @MethodSource("logins")
void login(String email, String pwd) {}

@TestFactory
Collection<DynamicTest> dyn() {
  return List.of(
    dynamicTest("sums to 3", () -> assertEquals(3, 1 + 2))
  );
}

Generate tests at runtime from data.

@RepeatedTest(10) void flakyGuard() {}

Great for catching intermittent race conditions in automation.

class LoginTest {
  WebDriver driver;
  @BeforeEach void up() { driver = new ChromeDriver(); }
  @AfterEach void down() { driver.quit(); }
  @Test void loginSucceeds() { /* ... */ }
}

See our Selenium Q&A bank.

@Test
void getUser() {
  given().baseUri("https://api.x.com")
    .when().get("/users/1")
    .then().statusCode(200)
    .body("email", containsString("@"));
}

Deep dives in our API Testing Q&A.

# src/test/resources/junit-platform.properties
junit.jupiter.execution.parallel.enabled=true
junit.jupiter.execution.parallel.mode.default=concurrent
junit.jupiter.execution.parallel.config.strategy=fixed
junit.jupiter.execution.parallel.config.fixed.parallelism=4

The replacement for JUnit 4's Runners and Rules. Implement callbacks like BeforeEachCallback, TestExecutionExceptionHandler. Common uses: screenshot-on-failure, Testcontainers, Spring integration.

junit.jupiter.execution.parallel.enabled=false

Then use Surefire's -Dsurefire.skipAfterFailureCount=1 to bail early — useful in smoke pipelines.

- run: mvn -B test
- uses: actions/upload-artifact@v4
  if: always()
  with: { name: surefire, path: target/surefire-reports/ }
- uses: mikepenz/action-junit-report@v4
  if: always()
  with: { report_paths: 'target/surefire-reports/*.xml' }