Test functions with JUnit where functions get user input

Question

First of all, I tried to look for some solution in this cool site. I have found a question relating to my issue, but my tests still fails. The question I found, can be found here: JUnit testing with simulated user input

Let's see my implementation:

I have an user interaction service class which read then validate the user inputs: UserInteractionService.java

package Services;

import java.util.Scanner;

public class UserInteractionService {

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

    public static int readIntegerAndValidate() {
        while (!scanner.hasNextInt()) {
            System.out.println("It is not a valid integer number. Try again!");
            scanner.next(); 
        }
        return scanner.nextInt();

    }

    public static double readDoubleAndValidate() {
        while (!scanner.hasNextDouble()) {
            System.out.println("It is not a valid number. Try again!");
            scanner.next(); 
        }
        return scanner.nextDouble();
    }
}

And, of course, I have a test class for this service class: UserInteractionServiceTest.java

@Test
public void userWriteInput_checkIfItIsInteger_userTypedInteger() {
    String inputData = "5";
    System.setIn(new ByteArrayInputStream(inputData.getBytes()));
    int input = readIntegerAndValidate();
    assertEquals(5, input);
}

@Test
public void userWriteDouble_checkIfItIsDouble_userTypedDouble() {
    String inputData = "5.3";
    System.setIn(new ByteArrayInputStream(inputData.getBytes()));
    double input = readDoubleAndValidate();
    assertEquals(5.3, input, 0);
}

Well, my second test function (userWriteDouble_checkIfItIsDouble_userTypedDouble) fails, and I could not find the reason... As you can see I used the same pattern like in de first test. What is your opinion, why does this test fail? Shall I use some mocking framework (Mockito)? Thanks in advance for the answers!

Failure Trace:

java.util.NoSuchElementException
    at java.util.Scanner.throwFor(Unknown Source)
    at java.util.Scanner.next(Unknown Source)
    at Services.UserInteractionService.readDoubleAndValidate(UserInteractionService.java:21)
    at Services.UserInteractionServiceTest.userWriteDouble_checkIfItIsDouble_userTypedDouble(UserInteractionServiceTest.java:23)
...

I would usually mock the Scanner, yes. What is the test failure output? — Willcodeforfun
– Willcodeforfun, Commented Apr 2, 2016 at 14:44
@Willcodeforfun Thanks for your comment! I edited my answer with the Failure Trace. So you say that mocking of scanner would be a good idea. How would the solution look like? — mirind4
– mirind4, Commented Apr 2, 2016 at 14:51
you said that the second test fails, does the first one pass? — Rahul Sharma
– Rahul Sharma, Commented Apr 2, 2016 at 14:57

Willcodeforfun · Accepted Answer · 2016-04-02 15:00:26Z

2

You've made it harder to test your code by making the scanner static. I would consider giving UserInteractionService a constructor that takes a Scanner. I suggest EasyMock and the code in test would look like

import static org.easymock.EasyMock.*;

Scanner scanner = createMock(Scanner.class);
expect(scanner.hasNextDouble()).and return(true).once();
expect(scanner.nextDouble()).and return(5.3).once();

replay(scanner);

And the service you call in your test would be a

new UserInteractionService (scanner)

answered Apr 2, 2016 at 15:00

Willcodeforfun

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2 Comments

mirind4 Over a year ago

Thanks! Well, it is not necessary to have a static scanner. Actually I use Mockito, so I try to solve it with this. I think I have to write almost the same with Mockito, so if it works, I will accept your answer! ;)

mirind4 Over a year ago

aah i have problem because I can not mock the Scanner class with Mocikto. With Mockito the static or final classes can not be mocked. I think I will change to BefferedReader in my implementation

Stefan Birkner · Accepted Answer · 2016-04-04 11:52:36Z

1

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.

answered Apr 4, 2016 at 11:52

Stefan Birkner

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3 Comments

mirind4 Over a year ago

Hey! Thanks for your answer, I upvoted it! Well, I have changed the code, but now the console waits for my input. It seems that the setIn() does not set value I gave to :\ What is your opinion? Thanks in advance for your help!

Stefan Birkner Over a year ago

You have to call setIn before you create the UserInteractionService. Are you doing it in this order?

mirind4 Over a year ago

Works like a charm! Thanks for the additional information! ;)

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