JUnit 5 User Guide

import static org.junit.jupiter.api.Assertions.fail;

import org.junit.jupiter.api.AfterAll;
import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Disabled;
import org.junit.jupiter.api.Test;

class StandardTests {

    @BeforeAll
    static void initAll() {
    }

    @BeforeEach
    void init() {
    }

    @Test
    void succeedingTest() {
    }

    @Test
    void failingTest() {
        fail("a failing test");
    }

    @Test
    @Disabled("for demonstration purposes")
    void skippedTest() {
        // not executed
    }

    @AfterEach
    void tearDown() {
    }

    @AfterAll
    static void tearDownAll() {
    }

}

import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;

@DisplayName("A special test case")
class DisplayNameDemo {

    @Test
    @DisplayName("Custom test name containing spaces")
    void testWithDisplayNameContainingSpaces() {
    }

    @Test
    @DisplayName("╯°□°）╯")
    void testWithDisplayNameContainingSpecialCharacters() {
    }

    @Test
    @DisplayName("😱")
    void testWithDisplayNameContainingEmoji() {
    }

}

import static org.junit.jupiter.api.Assertions.assertAll;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertTrue;
import static org.junit.jupiter.api.Assertions.expectThrows;

import org.junit.jupiter.api.Test;

class AssertionsDemo {

    @Test
    void standardAssertions() {
        assertEquals(2, 2);
        assertEquals(4, 4, "The optional assertion message is now the last parameter.");
        assertTrue(2 == 2, () -> "Assertion messages can be lazily evaluated -- "
                + "to avoid constructing complex messages unnecessarily.");
    }

    @Test
    void groupedAssertions() {
        // In a grouped assertion all assertions are executed, and any
        // failures will be reported together.
        assertAll("address",
            () -> assertEquals("John", address.getFirstName()),
            () -> assertEquals("User", address.getLastName())
        );
    }

    @Test
    void exceptionTesting() {
        Throwable exception = expectThrows(IllegalArgumentException.class, () -> {
            throw new IllegalArgumentException("a message");
        });
        assertEquals("a message", exception.getMessage());
    }

}

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assumptions.assumeTrue;
import static org.junit.jupiter.api.Assumptions.assumingThat;

import org.junit.jupiter.api.Test;

public class AssumptionsDemo {

    @Test
    void testOnlyOnCiServer() {
        assumeTrue("CI".equals(System.getenv("ENV")));
        // remainder of test
    }

    @Test
    void testOnlyOnDeveloperWorkstation() {
        assumeTrue("DEV".equals(System.getenv("ENV")),
            () -> "Aborting test: not on developer workstation");
        // remainder of test
    }

    @Test
    void testInAllEnvironments() {
        assumingThat("CI".equals(System.getenv("ENV")),
            () -> {
                // perform these assertions only on the CI server
                assertEquals(2, 2);
            });

        // perform these assertions in all environments
        assertEquals("a string", "a string");
    }

}

import org.junit.jupiter.api.Disabled;
import org.junit.jupiter.api.Test;

@Disabled
class DisabledClassDemo {
    @Test
    void testWillBeSkipped() {
    }
}

import org.junit.jupiter.api.Disabled;
import org.junit.jupiter.api.Test;

class DisabledTestsDemo {

    @Disabled
    @Test
    void testWillBeSkipped() {
    }

    @Test
    void testWillBeExecuted() {
    }
}

import org.junit.jupiter.api.Tag;
import org.junit.jupiter.api.Test;

@Tag("fast")
@Tag("model")
class TaggingDemo {

    @Test
    @Tag("taxes")
    void testingTaxCalculation() {
    }

}

@DisplayName("A stack")
class TestingAStackDemo {

    Stack<Object> stack;
    boolean isRun = false;

    @Test
    @DisplayName("is instantiated with new Stack()")
    void isInstantiatedWithNew() {
        new Stack<Object>();
    }

    @Nested
    @DisplayName("when new")
    class WhenNew {

        @BeforeEach
        void init() {
            stack = new Stack<Object>();
        }

        @Test
        @DisplayName("is empty")
        void isEmpty() {
            Assertions.assertTrue(stack.isEmpty());
        }

        @Test
        @DisplayName("throws EmptyStackException when popped")
        void throwsExceptionWhenPopped() {
            Assertions.expectThrows(EmptyStackException.class, () -> stack.pop());
        }

        @Test
        @DisplayName("throws EmptyStackException when peeked")
        void throwsExceptionWhenPeeked() {
            Assertions.expectThrows(EmptyStackException.class, () -> stack.peek());
        }

        @Nested
        @DisplayName("after pushing an element")
        class AfterPushing {

            String anElement = "an element";

            @BeforeEach
            void init() {
                stack.push(anElement);
            }

            @Test
            @DisplayName("it is no longer empty")
            void isEmpty() {
                Assertions.assertFalse(stack.isEmpty());
            }

            @Test
            @DisplayName("returns the element when popped and is empty")
            void returnElementWhenPopped() {
                Assertions.assertEquals(anElement, stack.pop());
                Assertions.assertTrue(stack.isEmpty());
            }

            @Test
            @DisplayName("returns the element when peeked but remains not empty")
            void returnElementWhenPeeked() {
                Assertions.assertEquals(anElement, stack.peek());
                Assertions.assertFalse(stack.isEmpty());
            }
        }
    }
}

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertTrue;

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Tag;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.TestInfo;

class TestInfoDemo {

    @BeforeEach
    void init(TestInfo testInfo) {
        String displayName = testInfo.getDisplayName();
        assertTrue(displayName.equals("TEST 1") || displayName.equals("test2()"));
    }

    @Test
    @DisplayName("TEST 1")
    @Tag("my tag")
    void test1(TestInfo testInfo) {
        assertEquals("TEST 1", testInfo.getDisplayName());
        assertTrue(testInfo.getTags().contains("my tag"));
    }

    @Test
    void test2() {
    }

}

import java.util.HashMap;

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.TestReporter;

class TestReporterDemo {

    @Test
    void reportSingleValue(TestReporter testReporter) {
        testReporter.publishEntry("a key", "a value");
    }

    @Test
    void reportSeveralValues(TestReporter testReporter) {
        HashMap<String, String> values = new HashMap<>();
        values.put("user name", "dk38");
        values.put("award year", "1974");

        testReporter.publishEntry(values);
    }

}

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.mockito.Mockito.when;

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.Mock;
import com.example.Person;
import com.example.mockito.MockitoExtension;

@ExtendWith(MockitoExtension.class)
class MyMockitoTest {

    @BeforeEach
    void init(@Mock Person person) {
        when(person.getName()).thenReturn("Dilbert");
    }

    @Test
    void simpleTestWithInjectedMock(@Mock Person person) {
        assertEquals("Dilbert", person.getName());
    }

}

public interface Testable<T> {

    T createValue();

}

public interface EqualsContract<T> extends Testable<T> {

    T createNotEqualValue();

    @Test
    default void valueEqualsItself() {
        T value = createValue();
        assertEquals(value, value);
    }

    @Test
    default void valueDoesNotEqualNull() {
        T value = createValue();
        assertFalse(value.equals(null));
    }

    @Test
    default void valueDoesNotEqualDifferentValue() {
        T value = createValue();
        T differentValue = createNotEqualValue();
        assertNotEquals(value, differentValue);
        assertNotEquals(differentValue, value);
    }

}

public interface ComparableContract<T extends Comparable<T>> extends Testable<T> {

    T createSmallerValue();

    @Test
    default void returnsZeroWhenComparedToItself() {
        T value = createValue();
        assertEquals(0, value.compareTo(value));
    }

    @Test
    default void returnsPositiveNumberComparedToSmallerValue() {
        T value = createValue();
        T smallerValue = createSmallerValue();
        assertTrue(value.compareTo(smallerValue) > 0);
    }

    @Test
    default void returnsNegativeNumberComparedToSmallerValue() {
        T value = createValue();
        T smallerValue = createSmallerValue();
        assertTrue(smallerValue.compareTo(value) < 0);
    }

}

class StringTests implements ComparableContract<String>, EqualsContract<String> {

    @Override
    public String createValue() {
        return "foo";
    }

    @Override
    public String createSmallerValue() {
        return "bar"; // 'b' < 'f' in "foo"
    }

    @Override
    public String createNotEqualValue() {
        return "baz";
    }

}

Test execution started. Number of static tests: 2
Engine started: junit-jupiter
Test started:     My 1st JUnit 5 test! 😎 [junit-jupiter:com.example.project.FirstTest#myFirstTest(java.lang.String)]
Test succeeded:   My 1st JUnit 5 test! 😎 [junit-jupiter:com.example.project.FirstTest#myFirstTest(java.lang.String)]
Test skipped:     mySecondTest [junit-jupiter:com.example.project.SecondTest#mySecondTest()]
                  => Exception:   Skipped test method [void com.example.project.SecondTest.mySecondTest()] due to failed condition
Engine finished: junit-jupiter
Test execution finished.

Test run finished after 29 ms
[         2 tests found     ]
[         1 tests started   ]
[         1 tests skipped   ]
[         0 tests aborted   ]
[         1 tests successful]
[         0 tests failed    ]

public class IgnoreIOExceptionExtension implements TestExecutionExceptionHandler {

    @Override
    public void handleTestExecutionException(TestExtensionContext context, Throwable throwable)
            throws Throwable {

        if (throwable instanceof IOException) {
            return;
        }
        throw throwable;
    }
}