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Module 3: Code Katas

This module will help get you in the habit of writing tests first.

Background

A code kata is a programming exercise in which a developer attempts to solve a pre-defined problem, to hone their skills.

Code katas are generally not real-world problems. They have well-defined specifications and rules.

Code katas are more about developing a practice, and less about solving the underlying problems. Katas are intended to help you build a testing habit. The more you practice TDD on sample problems, the sooner TDD becomes your default approach to real problems.

Ground Rules

  • Don't write new code without writing a test first
  • Do one task at a time; try not to read ahead
  • You are welcome to pair with others on this exercise!

Let's Play!

👉 Take a look at the module-3/add.spec.js test file. This is where you'll be writing your tests for this exercise.

Currently, there is one test, named it('exists'...). This test simply verifies that the add function exists.

Depending on your level of dogma, it is either very important to create a test that verifies the existence of a function before you write it, or very unimportant.

👉 Take a look at the module-3/add.js test file. This is where you'll be implementing your string calculator/add function.

Currently, you'll see that the function in add.js is returning undefined.

👉 Start up the test suite.

From a command line at the root of the workshop project, type npm run test-module-3. This will start up the test suite.

At this point, no tests should run, and you should see this message:

No tests found related to files changed since last commit.

👉 Start implementing the specifications!

The String Calculator kata

This kata builds a function that takes numbers in as string input, and returns their sum. It emphasizes refactoring.

The kata is adapted from http://osherove.com/tdd-kata-1.

Specifications

0. Note: You do not need to validate input. Assume all input into the method is valid.

1. Create a simple function add(string numbers)

This is done for you! There's even a test to verify that the function exists.

2. The function can take 0, 1 or 2 numbers.

Example inputs: “” or “1” or “1,2”

For an empty string the function should return 0.

For strings with 1 or 2 numbers, the function should return the sum of the numbers.

Suggestions:

  • Start with the simplest test case of an empty string and move to 1 and 2 numbers

  • Remember to solve things as simply as possible so that you force yourself to write tests you did not think about

  • Remember to refactor after each passing test

3. Allow the add function to handle an unknown amount of numbers, separated by commas

4. Allow the add function to handle new lines between numbers, instead of commas.

The following input is ok:  “1\n2,3”  (will equal 6)

The following input is NOT ok:  “1,\n” (You don't need to write a test for this - just clarifying.)

5. Support different delimiters

To specify a delimiter, the string will begin with two slashes, then the delimiter, then a new line.

For example, the input “//;\n1;2” should return three. "//;\n" specifies that the delimiter is ";", and "1;2" should be added together.

The delimiter specification is optional. All previously existing scenarios should still be supported.

6. Calling add with a negative number should throw an error with the message “Negatives not allowed: X”, where X is the negative value passed.

If there are multiple negatives, show all of them in the error message.

For example, the input "1,-1,-4" should throw the error "Negatives not allowed: -1, -4".