Unable to write Mockito test case for my void method

Question

I need to test this code with Mockito (JUnit):

public class Calculation {

    public void logTimeTaken(String label, long estimatedTime, int size, boolean isDebug) {
       String out = label + " took " + TimeUnit.MILLISECONDS.convert(estimatedTime, TimeUnit.NANOSECONDS) + " milliseconds for " + size + " events!";
        if (isDebug) {
            System.out.println(out);
        } else {
            System.out.println(out);
        }
    }
}

I search so many examples google but still not getting any idea.

Possible duplicate of [How to make mock to void methods with mockito](https://stackoverflow.com/questions/2276271/how-to-make-mock-to-void-methods-with-mockito) — Jonathan, May 31 '18 at 11:56

score 1 · Answer 1 · answered May 31 '18 at 11:47

You can configure System with an instance of PrintStream which you can then assert against after invoking Calculation.logTimeTaken.

Here's an example:

@Test
public void canLogTimeTaken() {
    ByteArrayOutputStream bout = new ByteArrayOutputStream();
    PrintStream out = new PrintStream(bout);
    System.setOut(out);

    Calculation sut = new Calculation();
    sut.logTimeTaken("label", 20 , 2, false);
    assertEquals("if isDebug is false label took 0 milliseconds for 2 events!\n", bout.toString());
}

Note: there is no need for Mockito here, this is just vanilla JUnit, no mocking.

But, it might be a better design to refactor logTimeTaken into two distinct aspects:

Deriving the log message
Logging that message

For example:

public String createTimeTakenMessage(String label, long estimatedTime, int size, boolean isDebug) {
    return label + " took " + TimeUnit.MILLISECONDS.convert(estimatedTime, TimeUnit.NANOSECONDS) + " milliseconds for " + size + " events!";
}

public void logTimeTaken(String message) {
    System.out.println(message);
}

Then testing createTimeTakenMessage is trivial and you might even choose not to test logTimeTaken at all since all it does is invoke a System method. Or, perhaps you would hide the 'log action' behind an interface with an implementation using System.out now and perhaps, later, other implementations using a formal logging framework such as Logback.

glyching,I used your code and run the program but my test is failed showing actual and excpected different,maually I checked spaces and spellings also but still test is failed can you help me how to solve this.. — srikanth, Jun 01 '18 at 03:30

Unable to write Mockito test case for my void method

1 Answers1