dice-tdd v1.2.2

dice-tdd

This module helps you learn TDD while writing a Node.js module.

Usage:

Check out this code. Ensure you are on master branch. Run npm test to see the tests fail. Your first failure will be due to the module dice.js being missing. Create an empty file called dice.js in the root of the project and you should see the full test suite run and fail.

Start by opening up test/dice-test.js and reading the tests. Tests all call the it() function. The first test looks like this:

it('Should return six', function() {
    expect(dice.roll()).to.equal(6);
});

See that it runs dice.roll() and expects the returned value to be 6. You can make this pass by adding this code to the dice.js module:

var roll = function() {
    return 6;
}

module.exports = {
    roll: roll
}

Save that file and re-run the test. You should have a passing test.

Explanation of what just happened:

You created one function called roll that simply returns the number 6. You then exported an object { } with a single value, roll, which was the roll function.

When you ran the test dice.roll() returned an acceptable value and the test passed.

Your goal:

Make all of your tests pass.

In the end you will have a dice module that rolls a dice. By default, it will be a six-sided dice (d6), but you can pass in a value to the roll() function that sets it to however many sides you want.

There will also be a rollHistory() method which shows you all the rolls, and a clearHistory() which, as you might guess, clears the roll history.

Mocks, helpers and proxy classes:

Your end result will use Math.random(). However, Math.random() cannot be mocked and you'll have weird, flaky tests if you don't mock it. To work around this, two things have been done:

• A proxy module called randomHelper.js was created. This exports a single function, so instead of using Math.random() instead use code like this:

  var random = require('./randomHelper');
  random();

In this case, random() will have exactly the same behavior as Math.random();

• There is a before() function defined in the tests, which runs before the first test is executed. It intercepts the call to require('./randomHelper') and replaces it with a stub function which always returns 0.99999. There is also an after() function which reverses this functionality.

Notice that in the second test we temporarily change the return value of the stub so that it returns 0.00001, checks the return value of the roll() function and then reverts the stub's behavior. This forces us to write smarter code.

How to check your work

There is a branch called completed which you can use to compare your work against my completed module. The easy way to review that code is to look at it here on Github, but you can also fetch that branch and review it locally.

Comments, questions and issues are welcome.