JUnit test for System.out.println()

Question

I need to write JUnit tests for an old application that\'s poorly designed and is writing a lot of error messages to standard output. When the getResponse(String reque

Answer 1

Slightly off topic, but in case some people (like me, when I first found this thread) might be interested in capturing log output via SLF4J, commons-testing's JUnit @Rule might help:

public class FooTest {
    @Rule
    public final ExpectedLogs logs = new ExpectedLogs() {{
        captureFor(Foo.class, LogLevel.WARN);
    }};

    @Test
    public void barShouldLogWarning() {
        assertThat(logs.isEmpty(), is(true)); // Nothing captured yet.

        // Logic using the class you are capturing logs for:
        Foo foo = new Foo();
        assertThat(foo.bar(), is(not(nullValue())));

        // Assert content of the captured logs:
        assertThat(logs.isEmpty(), is(false));
        assertThat(logs.contains("Your warning message here"), is(true));
    }
}

Disclaimer:

• I developed this library since I could not find any suitable solution for my own needs.
• Only bindings for log4j, log4j2 and logback are available at the moment, but I am happy to add more.