Junit test for println

Question

I'm trying to write junit tests for System.out, especially system.out.println, but even after reading through related posts, i couldn't get to the solutions.

public static void hello(){
    System.out.println("Hello");
}


@Test void Test(){
  System.setOut(new PrintStream(outContent));
  System.setErr(new PrintStream(errContent));

  hello();

  assertEquals("Hello\n" , outContent.toString());

  System.setIn(System.in);
  System.setOut(originalOut);
  System.setErr(originalErr);
}

It works perfectly fine when i use print instead of println and remove \n from assertEquals, but whenever i try println with \n, the test fails with

 expected: <Hello
> but was: <Hello
>
org.opentest4j.AssertionFailedError: expected: <Hello
> but was: <Hello
>

which even the error message looks the same. Is there any way i can use println and pass the test? Thank you

On which OS do you run this test? New lines differ per OS. See https://stackoverflow.com/a/1761086/2003874 — David Baak, Sep 17 '19 at 14:45

score 3 · Accepted Answer · answered Sep 17 '19 at 15:00

The problem is indeed the different line separators for Windows, I updated your fragment, I replaced \n with + System.lineSeparator()

Locally on my Mac it works I expect it to be fine on Windows too with this change.

public static void hello(){
    System.out.println("Hello");
}


@Test void Test(){
  System.setOut(new PrintStream(outContent));
  System.setErr(new PrintStream(errContent));

  hello();

  // Changed the line below  
  assertEquals("Hello" + System.lineSeparator(), outContent.toString());

  System.setIn(System.in);
  System.setOut(originalOut);
  System.setErr(originalErr);
}

Junit test for println

1 Answers1