readme.md

Mock loggers for SLF4J

SLF4J factory with mock loggers backed by Mockito.

Warning

This library does not support parallel test execution.

How to use

Just put a test dependency to your POM:

<dependency>
    <artifactId>mock-loggers-slf4j</artifactId>
    <groupId>io.github.vitalijr2.logging</groupId>
    <scope>test</scope>
    <version>1.0.0</version>
</dependency>

The simplest usage example looks like this:

@Test
void helloWorld() {
    var helloService = new HelloService();

    assertDoesNotThrow(helloService::sayHelloWorld);

    verify(LoggerFactory.getLogger(helloService.getClass())).info("Hello World!");
}

See more details at HelloServiceBasicTest.java

Important

Keep in mind that all loggers are initialized only once during the test run.

Therefore, a more complex example cleans the loggers after (or before) each test:

// the static logger instance
private static Logger logger;

// initialize the mock logger once
@BeforeAll
static void setUpClass() {
    logger = LoggerFactory.getLogger(HelloService.class);
}

// clean the mock logger after each test
@AfterEach
void tearDown() {
    clearInvocations(logger);
}

// use the mock logger in a test
@DisplayName("Names")
@ParameterizedTest(name = "<{0}>")
@ValueSource(strings = {"John", "Jane"})
void names(String name) {
    var helloService = new HelloService();

    assertDoesNotThrow(() -> helloService.sayHello(name));

    var actualLogger = LoggerFactory.getLogger(helloService.getClass());

    verify(actualLogger).info("Hello " + name + "!");
    verifyNoMoreInteractions(actualLogger);
}

See more details at HelloServiceFullTest.java

To avoid manual cleaning of mock loggers you can use the jUnit extension for automation.

@ExtendWith(MockLoggerExtension.class)
class HelloServiceExtensionTest {

    private static Logger logger;

    @BeforeAll
    static void setUpClass() {
        log = LogFactory.getLog(HelloService.class);
    }

    @DisplayName("Names")
    @ParameterizedTest(name = "<{0}>")
    @ValueSource(strings = {"John", "Jane"})
    void names(String name) {
        var helloService = new HelloService();

        assertDoesNotThrow(() -> helloService.sayHello(name));

        var actualLogger = LoggerFactory.getLogger(helloService.getClass());

        verify(actualLogger).info("Hello " + name + "!");
        verifyNoMoreInteractions(actualLogger);
    }

}

See more details at HelloServiceExtensionTest.java

Also you can use the annotation for automation.

@MockLoggers
class HelloServiceAnnotationTest {

    private static Logger logger;

    @BeforeAll
    static void setUpClass() {
        logger = LogFactory.getLog(HelloService.class);
    }

    @DisplayName("Names")
    @ParameterizedTest(name = "<{0}>")
    @ValueSource(strings = {"John", "Jane"})
    void names(String name) {
        var helloService = new HelloService();

        assertDoesNotThrow(() -> helloService.sayHello(name));

        var actualLogger = LogFactory.getLog(helloService.getClass());

        verify(actualLogger).info("Hello " + name + "!");
        verifyNoMoreInteractions(actualLogger);
    }

}

See more details at HelloServiceAnnotationTest.java