Test-Driven Development in Java/

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Writing Our Next Tests for Wordz

Writing Our Next Tests for Wordz

Learn how to incrementally add tests in Wordz for a single correct letter and engage in refactoring for clarity, readability, and simplification.

We'll cover the following...

So, what should we write for our next tests? What would be a useful and small enough step so that we don’t fall into the trap of writing beyond what our tests can support? In this lesson, we’ll continue building out the Wordz application scoring system using TDD. We’ll discuss how we choose to move forward at each step. For the next test, a good choice is to play it safe and move only a small step further.

We’ll add a test for a single correct letter. This will drive out our first piece of genuine application logic.

Writing a failing test for a single correct letter

Let’s start with red and write a failing test for a single correct letter.

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@Test
public void oneCorrectLetter() {
    var word = new Word("A");
    var score = word.guess("A");
    assertThat(score.letter(0))
    .isEqualTo(Letter.CORRECT);
}

This test is intentionally similar to the one before. The difference is that it tests for a letter being correct, rather than being incorrect. We’ve used the same word—a single letter, "A"—intentionally. This is important when writing tests—use test data that helps to tell the story of what we are testing and why. The story here is that the same word with a different guess will lead to a different score, which is obviously key to the problem we’re solving. Our two test cases completely cover both possible outcomes of any guess of a single-letter word.

Adding production code for passing the test

Now, let’s move to green by adding the production code to make the test pass:

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public class Word {
    private final String word;
    public Word(String correctWord) {
      this.word = correctWord;
    }
    public Score guess(String attempt) {
      var score = new Score(word);
      score.assess( 0, attempt );
      return score;
    }
}

The goal here is to get the new test to pass while keeping the existing test passing. We don’t want to break any existing code. We’ve added a field called word, which will store the word we are supposed to be guessing. We’ve added a public constructor to initialize this field. We’ve added code into the guess() method to create a new Score object. We’ve decided to add a method to this Score class called assess(). This method has the responsibility of assessing ...