Testing System.out.println Outputs 📎
Although System.out.println invocations might be buried deep inside static methods:
public class App {
public final static void main(String args[]) {
if (args.length != 2) {
usage();
return;
}
//...
}
static void usage() {
System.out.println("Use: java -jar airfield.App (...)");
}
}
...they are actually very easy to test by mocking-out the PrintStream:
import java.io.PrintStream;
import org.junit.Test;
import static org.mockito.Matchers.startsWith;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.verify;
public class AppTest {
@Test
public void mainUsage() {
PrintStream out = mock(PrintStream.class);
System.setOut(out);
App.main(new String[]{});
verify(out).println(startsWith("Use:"));
}
}
The example above was extracted from the: airfield and loadr projects.
See you at the Java 8 and Java EE 7 Testing andn Quality workshop at MUC Airport.