A First Look at the Newly Released JUnit 5

In July, the first milestone of JUnit 5 was released. This new version will make use of Java 8 lambdas and will redesign some JUnit core features.

What’s New

Some of the main changes affecting how we’ll write JUnit tests are:

• New package org.junit.jupiter.api — instead of good old org.junit
• @BeforeEach, @BeforeAll, @AfterEach, @AfterAll — instead of the ones we use now
• @Disabled to disable tests — instead of @Ignored
• @ExtendedWith supersedes @RunWith and @Rule
• DynamicTests supersede Parameterized tests
• Assertions#expectThrows for expected exceptions

The 5.0.0-M1 version can be used from Maven central:

<dependencies>
    <dependency>
        <groupId>org.junit.jupiter</groupId>
        <artifactId>junit-jupiter-engine</artifactId>
        <version>5.0.0-M1</version>
        <scope>test</scope>
    </dependency>
</dependencies>

...

<plugins>
    <plugin>
        <artifactId>maven-surefire-plugin</artifactId>
        <version>2.19.1</version>
        <dependencies>
            <dependency>
                <groupId>org.junit.platform</groupId>
                <artifactId>junit-platform-surefire-provider</artifactId>
                <version>1.0.0-M1</version>
            </dependency>
        </dependencies>
    </plugin>
</plugins>

How to Use

Here is an example of a functionality and its test:

public class FunWithStrings {

    public String getStringLength(final String string) {
        return string + ':' + string.length();
    }

}

public class FunWithStringsTest {

    private FunWithStrings cut = new FunWithStrings();

    // first, simple test
    @Test
    public void testGetStringLengthSimpleTest() {
        assertEquals("hello:5", cut.getStringLength("hello"), () -> "'hello' (length: 5) wasn't calculated properly");
    }

    @TestFactory
    public Stream<DynamicTest> createGetStringLengthTests() {
        final String[][] data = {
                // input, expected
                {"hello", "hello:5"},
                {"hel", "hel:3"},
                {"h", "h:1"},
                {"", ":0"},
                {" ", " :1"}
        };

        return Stream.of(data).map(o -> dynamicTest("test: " + o[0], () -> assertEquals(o[1], cut.getStringLength(o[0]))));
    }

    @Test
    public void testNull() {
        expectThrows(NullPointerException.class, () -> cut.getStringLength(null));
    }

}

The method annotated with @TestFactory is not a test itself but creates a stream of dynamic tests—in this usage, similar to the idea of Parameterized tests of JUnit 4.

The following example shows how more sophisticated test scenarios could be realized. Imagine a system test scenario testing a resource which is available only after some startup time. The test should wait within a timeout for the resource being available.

Prior to JUnit 5, this could be realized with an @Rule.

@ExtendWith(MockedSystemExtension.class)
public class SystemTest {

    @Test
    public void test(final MockedSystem mockedSystem) {
        final Response response = mockedSystem.target().request().get();

        assertEquals(response.getStatusInfo().getFamily(), Response.Status.Family.SUCCESSFUL, () -> "status code is not 2xx");
        assertEquals(response.getHeaderString("X-Hello"), "World", () -> "header 'X-Hello' not correct");
    }

}

The MockedSystem can be injected in the test method due to the registered extension:

public class MockedSystemExtension implements ParameterResolver {

    @Override
    public boolean supports(final ParameterContext parameterContext, final ExtensionContext extensionContext) throws ParameterResolutionException {
        return parameterContext.getParameter().getType().isAssignableFrom(MockedSystem.class);
    }

    @Override
    public Object resolve(final ParameterContext parameterContext, final ExtensionContext extensionContext) throws ParameterResolutionException {
        final MockedSystem mockedSystem = new MockedSystem();

        waitForStartUp(mockedSystem);

        return mockedSystem;
    }

    private void waitForStartUp(MockedSystem mockedSystem) {
        // ...
    }

}

The system simulates a WebTarget which normally would be used to access an API.

Here I use Mockito to simulate a system that takes 10 seconds to start up:

public class MockedSystem {

    private static final int STARTUP_TIME = 10;

    private final WebTarget target;

    MockedSystem() {
        final WebTarget tut = mock(WebTarget.class);
        final Invocation.Builder builder = mock(Invocation.Builder.class);
        final Response notFoundResponse = mock(Response.class);
        final Response okResponse = mock(Response.class);
        final long start = System.currentTimeMillis();

        when(tut.request()).thenReturn(builder);
        when(builder.get()).then(a -> {
            if (System.currentTimeMillis() - start < STARTUP_TIME * 1000)
                return notFoundResponse;
            return okResponse;
        });

        when(notFoundResponse.getStatus()).thenReturn(404);
        when(notFoundResponse.getStatusInfo()).thenReturn(Response.Status.NOT_FOUND);

        when(okResponse.getStatus()).thenReturn(200);
        when(okResponse.getStatusInfo()).thenReturn(Response.Status.OK);
        when(okResponse.getHeaders()).thenReturn(new MultivaluedHashMap<>(Collections.singletonMap("X-Hello", "World")));
        when(okResponse.getHeaderString(anyString())).then(a -> ((Response) a.getMock()).getHeaders().getFirst(a.getArgument(0)));

        this.target = tut;
    }

    public WebTarget target() {
        return target;
    }

}

Therefore, the SystemTest can count on the fact that the injected MockedSystem was probed so it can be available before—transparent to the test class itself.

Further Reading

These snippets are taken from my JUnit 5 Playground Github project.

Also, see the JUnit 5 User Guide.

Happy testing!