如何测试仅打印消息的方法

Question

I have method that print winner in the class Game:

public void getWinner(String winner){

   System.out.println("WINNER IS " + winner);

}

How can I test this method so far I have:

Game gm = new Game(); // it is declared in @before

@test

public void test(){

  ByteArrayOutputStream outContent = new ByteArrayOutputSystea();

  System.setOut(new PrintStream(outContent));

  gm.getWinner(Bob);

  assertEquals("WINNER IS Bob",outContent.toString());

}

I have an error message that say

org.unit.ComparisonFailuter expected:<WINNER IS Bob[]> but was: <WINNER IS Bob[
]>

Well could you please give me a tip on how to test getWinner method

Answer 1

omg don't do it! you don't have to test the println method. guys from sun and oracle have already done that - you can be sure it works. all you have to test is that you pass the right string to to that method. so refactor your code and create a function that return the desired string and test only that method by simple string comparison

Answer 2

From the documentation :

public void println(String x)

Prints a String and then terminate the line. This method behaves as though it invokes print(String) and then println().

So when you print the line in the method, there's a line separator after it which is defined as so:

The line separator string is defined by the system property line.separator, and is not necessarily a single newline character ('\\n').

So you can either add a hardcoded line separator to your expected output, or you could use the following code to get the separator for the current system and append that.:

System.getProperty("line.separator");

Answer 3

A mockist approach:

@Test
public void testGetWinner()
    {
    // setup: sut
    Game game = new Game();
    PrintStream mockPrintStream = EasyMock.createMock(PrintStream.class);
    System.setOut(mockPrintStream);

    // setup: data
    String theWinnerIs = "Bob";

    // setup: expectations
    System.out.println("WINNER IS " + theWinnerIs);

    // exercise
    EasyMock.replay(mockPrintStream);
    game.getWinner(theWinnerIs);

    // verify
    EasyMock.verify(mockPrintStream);
    }

Pro: You don't need to care what System.out.println() does, in fact if the implementation changes your test will still pass.

Answer 4

I think you try to compare to strings with == when you should use .equals() . The strings are stored ia constant pool, but in this case you read a string from somewhere else, which not nescessarily goes into the constant pool.

Try

assertTrue(outContent.toString().equals("WINNER IS Bob"));

or whatever your testing library calls it.

which looks for the characters in the String instead of the memory address ("ref") of the String.