Test Driven Development with Trees in Jasmine

Setting up jasmine

Jasmine is a node.js library. If you're just running this project, all you'll need to do is clone it down and run npm install in the base directory, and npm install -g jasmine to be able to run the jasmine command to run tests.

If you're setting up jasmine for an existing project, check out the docs for more detailed info.

If you are starting a node project from scratch to try out jasmine, you'll want a package.json file -- if you want info on how to generate one, take a look at these docs.

Test Driven Development

what is it?
- start with requirements
- write tests for the behaviors you care about
- then write the function
- often jumping back and forth between implementation and writing more tests
- The process is often described as red, green, refactor (start with writing a failing test, then write code to pass the test, then make the code better)
when is it useful?
- when requirements are clear-cut and known ahead of time
- when there's tricky logic involved
- when there are edge cases that might fall through the cracks
- when you find yourself repeatedly going through the same motions to manually test something
when is it less ideal?
- when you're not sure about the final requirements yet
  - design decisions not yet made
  - not sure what kinds of input to expect
  - quick and dirty prototyping that you expect to scrap
- when it's legitimately a better time/attention trade-off to manually test every time than to write an automated test
  - e.g. testing behavior of a web page element after an ajax call
- when it's difficult to stub out integrated systems

Note that writing comprehensive tests up front is often a difficult target -- if you intend to use TDD for a project but find that you've gotten partway through the project without any tests, it's often a good idea to add some even if they don't cover all the edge cases.

Whether or not you're taking a TDD approach, if you ever find a bug in the course of manual testing, try to write a test that will fail with the bug in place and pass once it's fixed!

TDD with Jasmine

Jasmine and some other testing frameworks (like rspec) tend to try to have the syntax work out such that each test reads like a sentence. You can take a look at some of the syntax here.

describe("A suite", function() {
  it("contains spec with an expectation", function() {
    expect(true).toBe(true);
  });
});

The main building blocks are describe blocks which serve to group tests and define local scope, it blocks which define a specific test or set of tests (also known as specs), and expect blocks which actually check that the code is behaving as desired using matchers.

When using toBe and toEqual matchers, you should put the code you want to exercise on the left (as a parameter to expect) and the value you expect it to evaluate to on the right (as a parameter to the matcher).

Running Jasmine tests

Assuming you've set up your jasmine.json file, you can run all of your Jasmine tests with just the command jasmine. If you only want to run the tests in a single file, you can run jasmine followed by the path to that file. You can also specify other options in the jasmine.json file, such as whether to run tests in random order, stop running the test once a spec fails, or or stop running an indivdiual test when an expect fails.

Trees