Install with maven

<dependency>
    <groupId>io.github.hakky54</groupId>
    <artifactId>logcaptor</artifactId>
    <version>1.1.0</version>
    <scope>test</scope>
</dependency>

Introduction

LogCaptor is a library which will enable you to easily capture logging entries for unit testing purposes.

Tested Logging libraries

• Log4j with Apache
• Log4j with Lombok
• Log4j2 with Lombok
• Slf4j with Lombok
• Java Util Logging with Lombok

See the unit test LogCaptorShould for all the scenario's

Supported Java versions

• Java 8
• Java 11+

Usage

To be tested class

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

public class FooService {

    private static final Logger LOGGER = LogManager.getLogger(FooService.class);

    public void sayHello() {
        LOGGER.info("Keyboard not responding. Press any key to continue...");
        LOGGER.warn("Congratulations, you are pregnant!");
    }

}

Unit test:

import static org.assertj.core.api.Assertions.assertThat;

import ch.qos.logback.classic.Level;
import nl.altindag.log.LogCaptor;
import org.junit.Test;

public class FooServiceShould {

    @Test
    public void logInfoAndWarnMessages() {
        String expectedInfoMessage = "Keyboard not responding. Press any key to continue...";
        String expectedWarnMessage = "Congratulations, you are pregnant!";

        LogCaptor<FooService> logCaptor = LogCaptor.forClass(FooService.class);

        FooService fooService = new FooService();
        fooService.sayHello();

        // Option 1 to assert logging entries
        assertThat(logCaptor.getLogs(Level.INFO)).containsExactly(expectedInfoMessage);
        assertThat(logCaptor.getLogs(Level.WARN)).containsExactly(expectedWarnMessage);

        // Option 2 to assert logging entries
        assertThat(logCaptor.getLogs("INFO").containsExactly(expectedInfoMessage);
        assertThat(logCaptor.getLogs("WARN").containsExactly(expectedWarnMessage);

        // Option 3 to assert logging entries
        assertThat(logCaptor.getLogs())
                .hasSize(2)
                .containsExactly(expectedInfoMessage, expectedWarnMessage);
    }
}

Class which will log events if specific log level has been set

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

public class FooService {

    private static final Logger LOGGER = LogManager.getLogger(FooService.class);

    public void sayHello() {
        if (LOGGER.isDebugEnabled()) {
            LOGGER.debug("Keyboard not responding. Press any key to continue...");
        }
        LOGGER.info("Congratulations, you are pregnant!");
    }

}

Unit test:

import static org.assertj.core.api.Assertions.assertThat;

import ch.qos.logback.classic.Level;
import nl.altindag.log.LogCaptor;
import org.junit.Test;

public class FooServiceShould {

    @Test
    public void logInfoAndWarnMessages() {
        String expectedInfoMessage = "Congratulations, you are pregnant!";
        String expectedDebugMessage = "Keyboard not responding. Press any key to continue...";

        LogCaptor<FooService> logCaptor = LogCaptor.forClass(FooService.class);
        logCaptor.setLogLevel(Level.INFO);

        FooService fooService = new FooService();
        fooService.sayHello();

        assertThat(logCaptor.getLogs(Level.INFO)).containsExactly(expectedInfoMessage);
        assertThat(logCaptor.getLogs(Level.DEBUG))
            .doesNotContain(expectedDebugMessage)
            .isEmpty();
    }
}

License