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Writing More Tests With the Bowling Game Kata

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rustttam edited this page Oct 1, 2020 · 4 revisions

The Bowling Game Kata refers to a test-driven development practice exercise recommended by Robert C. Martin or, as he is often referred to, Uncle Bob. You can find his version of it here: http://butunclebob.com/ArticleS.UncleBob.TheBowlingGameKata

We will progress through the exercise similarly to the Java version, using UnitTest++. To summarize, our goal is to create a class Game that has two methods:

  • roll(pins : int) which is called each time the ball is rolled; pins is the number of pins knocked down.
  • score() : int is called at the end of the game, returning the total score.

For simplicity's sake, I will be putting the Game class and the test cases in a single file.

The First Test

In our first test, we'll verify that a gutter game (20 gutter balls) scores a total of zero. First we create our Game class and our test suite:

#include "UnitTest++/UnitTest++.h"

class Game
{ 
};

SUITE(BowlingGameTest)
{
    TEST(GutterGame)
    {
        Game g;
    }
}

The SUITE macro introduces a bundled set of tests. While not strictly required by UnitTest++, suites can be used to annotate and organize your tests, and to selectively run them. The TEST macro, as previous introduced, is the actual test case; right now it isn't asserting anything. Let's add the actual test.

SUITE(BowlingGameTest)
{
    TEST(GutterGame)
    {
        Game g;
        
        for (int i = 0; i < 20; ++i)
        {
            g.roll(0);
        }
        
        CHECK_EQUAL(0, g.score());
    }
}

This will fail to compile until we add the requisite methods to game, so let's do that:

class Game
{
public:
    void roll(int pins)
    {
    }
    
    int score() const
    {
        return -1;
    }
};

Now we build and run and we have a failure:

TheFirstTest.cpp:27:1: error: Failure in GutterGame: Expected 0 but was -1
FAILURE: 1 out of 1 tests failed (1 failures).

Now, obviously we know more about our final implementation than this, but for now we can "fake it" to make the build succeed by changing score to return 0. We end up with the full code below:

#include "UnitTest++/UnitTest++.h"

class Game
{
public:
    void roll(int pins)
    {
    }
    
    int score() const
    {
        return 0;
    }
};

SUITE(BowlingGameTest)
{
    TEST(GutterGame)
    {
        Game g;
        
        for (int i = 0; i < 20; ++i)
        {
            g.roll(0);
        }
        
        CHECK_EQUAL(0, g.score());
    }
}

The test passes and we're ready to move on to Macro and Parameter Reference.

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