Logger with mockito in java

Question

I'm trying to verify a logger message with mockito.

However, I can not run my junit class to coverage all lines of code.

Do you know the reason why?

My code:

    public class App {
      private static final Logger LOGGER = Logger.getLogger(App.class);

      public List<String> addToListIfSizeIsUnder3(final List<String> list, final String value) {
        if (list == null) {
            LOGGER.error("A null list was passed in");
            return null;
        }
        if (list.size() < 3) {
            list.add(value);
        } else {
            LOGGER.debug("The list already has {} entries"+ list.size());
        }
        return list;
    }
}

My JUnit class

import static org.mockito.Mockito.times;
import static org.mockito.Mockito.verify;

import java.util.ArrayList;
import java.util.List;

import org.apache.log4j.Appender;
import org.apache.log4j.Level;
import org.apache.log4j.Logger;
import org.apache.log4j.spi.LoggingEvent;
import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.ArgumentCaptor;
import org.mockito.Captor;
import org.mockito.Mock;
import org.mockito.runners.MockitoJUnitRunner;

@RunWith(MockitoJUnitRunner.class)
public class AppTest {
    private App uut;
    @Mock
    private Appender mockAppender;
    @Captor
    private ArgumentCaptor<LoggingEvent> captorLoggingEvent;

    @Before
    public void setup() {
        uut = new App();

        Logger root = Logger.getRootLogger();
        root.addAppender(mockAppender);
        root.setLevel(Level.INFO);
    }

    /**
     * I want to test with over 3 elements.
     */
    @Test
    public void testWithOver3Element() {
        List<String> myList = new ArrayList<String>();
        myList.add("value 1");
        myList.add("value 2");
        myList.add("value 3");
        myList.add("value 4");
        List<String> outputList = uut.addToListIfSizeIsUnder3(myList, "some value");
        Assert.assertEquals(4, outputList.size());
        Assert.assertFalse(myList.contains("some value"));

try {
            verify(mockAppender, times(1)).doAppend(captorLoggingEvent.capture());
        } catch (AssertionError e) {
            e.printStackTrace();
        }

        LoggingEvent loggingEvent = captorLoggingEvent.getAllValues().get(0);
        Assert.assertEquals("The list already has {} entries", loggingEvent.getMessage());
        Assert.assertEquals(Level.DEBUG, loggingEvent.getLevel());
    }
}

ERROR:

Wanted but not invoked: mockAppender.doAppend(); -> at AppTest.testWithOver3Element(AppTest.java:52) Actually, there were zero interactions with this mock.

at AppTest.testWithOver3Element(AppTest.java:52) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229) at org.junit.runners.ParentRunner.run(ParentRunner.java:309) at org.mockito.internal.runners.JUnit45AndHigherRunnerImpl.run(JUnit45AndHigherRunnerImpl.java:37) at org.mockito.runners.MockitoJUnitRunner.run(MockitoJUnitRunner.java:62) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)

Answer 1

Although a valid answer has already been provided, I want to propose an alternative where you don't need to expose the Logger for mocking and you don't need to use mocking at all. It works for both SLF4J API and Log4J2 API.

See here for the library https://github.com/Hakky54/log-captor

Include in your maven file the reference for the library:

<dependency>
    <groupId>io.github.hakky54</groupId>
    <artifactId>logcaptor</artifactId>
    <version>2.6.1</version>
    <scope>test</scope>
</dependency>

In java code test method you should include this:

LogCaptor logCaptor = LogCaptor.forClass(App.class);

 // do the test logic....

assertThat(logCaptor.getLogs()).contains("Some log to assert");