Junit Test for InputStreamReader with Mockito

Question

Can you please help me in writing the Junit test case for the below code?

public class ConsoleReader implements InputReader {
    public Cell readInput() {
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
            System.out.print("Enter the co-ordinate Seperated by Comma");
            String coOrdinates = reader.readLine();
            String[] values=coOrdinates.split("\\,");
            return new Cell(Integer.parseInt(values[0]),Integer.parseInt(values[1]));
        } catch (IOException ioe) {
            ioe.printStackTrace();
        }
        return null;
    }
}

Insteed of `new InputStreamReader(System.in)` pass `System.in` as method argument so you will be able to actually push data into the stream. — Antoniossss, Nov 20 '18 at 12:10
Possible duplicate of [Mocking Java InputStream](https://stackoverflow.com/questions/6371379/mocking-java-inputstream) — Renny, Nov 20 '18 at 13:01
as Antoniossss has suggested the best solution (even from design perspective). if you dont like that solution , there is a tricky/dirty solution. use the System.setIn and set a mock inputstream , once your test case is executed restore the system.in using the same method. this will work only in environment you dont have securitymanger or you have permission to setIO — hunter, Nov 20 '18 at 13:57

ETO · Answer 1 · 2020-04-16T14:47:35.590

Extract the reader as a field. (You can initiaize it either directly or in constructor)

private final BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

Define a getter (either public or protected)

protected BufferedReader getReader(){
    return reader;
}

Remove initialization of new BufferedReader(...) from your method. Retrieve it using getReader() instead.

public Cell readInput() {
    try {
        System.out.print("Enter the co-ordinate Seperated by Comma");
        String coOrdinates = getReader().readLine();
        String[] values=coOrdinates.split("\\,");
        return new Cell(Integer.parseInt(values[0]),Integer.parseInt(values[1]));
    } catch (IOException ioe) {
        ioe.printStackTrace();
    }
    return null;
}

In your test class initialize your ConsoleReader as Mockito.spy
```
ConsoleReader consoleReader = spy(new ConsoleReader());
```

Mock your getter

private BufferedReader bufferedReader = mock(BufferedReader.class);

@Before
public void setUp() {
    doReturn(bufferedReader).when(consoleReader).getReader();
    doCallRealMethod().when(consoleReader).readInput();
}

Define your test:

@Test
public void testReadInput() {
    when(bufferedReader.readLine()).thenReturn("123,456");

    Cell expectedCell = new Cell(123, 456);
    Cell actualCell = consoleReader.readInput();

    assertEquals(expectedCell, actualCell);   
}

score 1 · Accepted Answer · answered Nov 20 '18 at 12:33

1

You can use Mockito to mock the BufferedReader, like the example below.

BufferedReader bufferedReader = Mockito.mock(BufferedReader.class);
Mockito.when(bufferedReader.readLine()).thenReturn("1", "2", "3");
// You can mock the result based on the type of result you are expecting.

answered Nov 20 '18 at 12:33

joemokenela

299
1
9

2

But he must pass that mock first. – Antoniossss Nov 20 '18 at 12:37

Junit Test for InputStreamReader with Mockito

2 Answers2