Testing

Writing Tests

As a totally new way of thinking, we'll start by writing testSort() first, and only after we've finished the test, we'll move on to writing the actual sorting code.

Ad Hoc Testing

We simply need to create an input, call sort, and check that the output of the method is correct. If the output is not correct, we print out the first mismatch and terminate the test.

public class TestSort {
  /** Tests the sort method of the Sort class. */
  public static void testSort() {
    String[] input = {"i", "have", "an", "egg"};
    String[] expected = {"an", "egg", "have", "i"};
    Sort.sort(input);
    for (int i = 0; i < input.length; i += 1) {
      if (!input[i].equals(expected[i])) {
        System.out.println("Mismatch in position " + i + ", expected: " + expected + ", but got: " + input[i] + ".");
        break;
      }
    }
  }

  public static void main(String[] args) {
    testSort();
  }
}

JUnit Testing

import static org.junit.Assert.*;
public class TestSort {
  /** Tests the sort method of the Sort class. */
  public static void testSort() {
    String[] input = {"cows", "dwell", "above", "clouds"};
    String[] expected = {"above", "clouds", "cows", "dwell"};
    Sort.sort(input);

    assertEquals(input, expected);
  }

  public static void main(String[] args) {
    testSort();
  }
}

Integration Testing

Integration testing verifies that components interact properly together.

Testing in IDE

If we add @Test before a method AND make the function non-static, green arrows appear.

public class TestSort {
  @Test
  public void testSort() { ... %%  %%}
}

• The single green arrow by testSort means “run this function”.
• The double green arrow means run all tests in this class.

Test-Driven Development (TDD)

TDD is a development process in which we write tests for code before writing the code itself. The steps are as follows:

1. Identify a new feature.
2. Write a unit test for that feature.
3. Run the test. It should fail.
4. Write code that passes the test. Yay!
5. Optional: refactor code to make it faster, cleaner, etc. Except now we have a reference to tests that should pass.

Test-Driven Development is not required in this class and may not be your style but unit testing in general is most definitely a good idea.