PrintArrayTest.java

PrintArrayTest.java

public class PrintArrayTest {

  interface Display {
    void print(String message);
  }

  public void printArray(int[] array, Display display) {
    int index = 0;
    for (int item : array) {
      display.print("array[" + index + "]=" + item + ",");
      index++;
    }

  }

  class InMemoryDisplay implements Display {

    private StringBuilder printedMessages = new StringBuilder();

    public void print(String message) {
      printedMessages.append(message);
    }

    private void assertHasPrintedMessage(String expectedMessage) {
      assertThat("the displayed message in the display was different from expected?",printedMessages.toString(), is(equalTo(expectedMessage)));
    }
  }

  @Test
  public void printArray() {
    InMemoryDisplay display = new InMemoryDisplay();
    printArray(new int[] {1, 2}, display);
    display.assertHasPrintedMessage("array[0]=1,array[1]=2,");
  }

}

1- what is the use of the interface here ? As you can see, the interface is used to fake (read more about mock,fakes,stubs and etc) the real console output, so I can assert the printed content. I used it to show you that my test is shorter then your test. In fact, the same behavior could be achieved and by using a simple PrintWriter (System.out is instance of PrintWriter). For example public void printArray(int[] array, PrintWriter writer) { ... } So to test it, we could use something like: ByteArrayOutputStream bout = new ByteArrayOutputStream(); PrintWriter writer = new PrintWriter(bout); printArray(new int[] { 1, 2, 3} , writer); // we need to call flush to be sure that all content is written to the output stream writer.flush(); String actual = new String(bout.toByteArray()); assertThat(actual,is(equalTo(expected)); As you can see, there is no additional interface and etc, but the problem here is that if I want to test a scenario where the data cannot be printed you have to do some magic around ByteArrayOutputStream to throw IOException, where in my case with interface I can mock the interface using jmock/easymock/mockito or any other mocking library to simulate the error behavior. 2- why did you re-implement printArray this way ? i mean printArray PRINTS (DISPLAYS ON THE SCREEN ), but this one is appending to StringBuilder object created in InMemoryDisplay Class ? I used an fake implementation named InMemoryDisplay, to simulate the real console output writer, so I can assert the response. The problem with your test is that the System.out is tight coupled with the definition in your method. To fix that I extracted that dependency as a method parameter. 3- why the assertion method is part of InMemoryClass not part of printArray Nothing obligates me to insert my assertions in the test method. I prefer that way, cause I don't have to write a similar assert in all of my test methods, i.e removing code duplication. 4- why you don't follow the naming convention of JUnit as it is mentioned in the books ? or this is up to you since there is the @test annotation? JUnit 3 requires that, but you are using JUnit 4 which requires @test annotation only. I think that the word "test" in front of your test doesn't gives you more information about what you are verifying. The most of the books are junit 3 related, that's why the examples are starting with "test". 5- Too may question, sorry :) Yeah, too many for few lines of code :)

On Tue, Jul 5, 2011 at 1:58 AM, fireball183 < ***@***.***>wrote: Here are some questions that i hope to get clear answer or direct links or notes otherwise 1- what is the use of the interface here ? 2- why did you re-implement printArray this way ? i mean printArray PRINTS (DISPLAYS ON THE SCREEN ), but this one is appending to StringBuilder object created in InMemoryDisplay Class ? 3- why the assertion method is part of InMemoryClass not part of printArray 4- why you don't follow the naming convention of JUnit as it is mentioned in the books ? or this is up to you since there is the @test annotation? 5- Too may question, sorry :) ## Reply to this email directly or view it on GitHub: https://gist.github.com/1058129

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