Mock User Console Input in Junit Test

How can I test against console input automaticly by mocking?

Please take a look at the example:

@RunWith(MockitoJUnitRunner.class)
public class TestClass {
   @Mock
   ConsoleReaderWriter crw;

   @InjectMocks
   UnderTestClass underTest;

   //Some other fields

   @Test
   public void testReadPlayerNameShouldReturnNameString() {
      String testName = "John Doe";

      when(crw.readLine()).thenReturn("John Doe");

      assertEquals(testName, underTest.readPlayerName());
   }
}

JUnit testing with simulated user input

You can replace System.in with you own stream by calling System.setIn(InputStream in).
InputStream can be a byte array:

InputStream sysInBackup = System.in; // backup System.in to restore it later
ByteArrayInputStream in = new ByteArrayInputStream("My string".getBytes());
System.setIn(in);

// do your thing

// optionally, reset System.in to its original
System.setIn(sysInBackup);

Different approach can be make this method more testable by passing IN and OUT as parameters:

public static int testUserInput(InputStream in,PrintStream out) {
    Scanner keyboard = new Scanner(in);
    out.println("Give a number between 1 and 10");
    int input = keyboard.nextInt();

    while (input < 1 || input > 10) {
        out.println("Wrong number, try again.");
        input = keyboard.nextInt();
    }

    return input;
}

JUnit test for console input and output

Ideally, extract the awkward dependencies so that you can test without them. Change main to simply:

public static void main(String[] args) {
  doWork(new Scanner(System.in), System.out);
}

// TODO: Rename to something meaningful
public static void doWork(Scanner input, PrintStream output) {
  // Remainder of code
}

(Consider using a Writer instead of a PrintStream for output.)

Then you don't really need to unit test main - but you can test doWork using a Scanner based on a StringReader, and output based on a StringWriter, providing whatever input you want and checking the output.

JUnit test user input with Mockito

You need to Mock BufferedReader's readLine() API to return your value.
i.e

 Mockito.when(mockedBufferedReader.readLine())
                .thenReturn("1");

Now when you call the readInput() from the Test then your mocked buffered reader's API will be invoked.Hope this answers your question.

Test functions with JUnit where functions get user input

Don't use a static field for the Scanner. It stores the reference to the System.in when it is created the first time. Setting System.in again to a different value in the second test does not change the Scanner's System.in. Change your class code like this fixes your test.

private Scanner scanner = new Scanner(System.in);

By the way you should restore System.in after the test. I've written a library named System Rules that makes it even easier to write tests for code that reads from System.in.

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