How should I test a Rails application with RSpec to get complete test coverage?

Question

When writing specs for a simple Rails app, is the following a correct approach for full test coverage?

1. Write feature specs for all user stories
2. Write controller specs to ensure that individual action responses are correct and all required variables are set
3. Write model specs to ensure all methods, validations,e tc. are working as intended
4. Write mailer specs
5. Write routing specs

Is this enough, too much (e.g. can I skip some lower-level specs if I've written feature specs), or not enough? Why?

Answer 1

You don't need to write specs for every object in every layer either to get 100% test coverage or to test-drive (require you to implement) all of the important behavior in your application. Instead, as behavior-driven development (BDD) advises, write specs outside in, and write lower-level specs only as necessary.

The most important measure of test completeness is requirement coverage: it's helpful for each user story, and each detail of each story that requires new code, to be represented in at least one test. If you're following typical agile practices (mentioning user stories suggests that you are) your tests are probably the only place where you record your requirements, so you probably can't put a number on this kind of coverage. It's also helpful to have

• line coverage (what most people mean when they say test coverage), meaning that every line of code is exercised by at least one test, and
• integration coverage, meaning that every method call from one class to another is exercised by at least one test.

For each story,

• Write only the feature specs that will test-drive all of the story's distinct happy paths.
• Write additional feature specs to ensure integration coverage of architecturally interesting minor variations of happy paths and of sad paths. For example, I often write three feature specs for a story that involves a form: one where the user fills in every possible field and succeeds, another where the user fills in as little information as possible and still succeeds (ensuring that unspecified values and defaults work as intended), and one where the user makes a mistake, fails, corrects the mistake and succeeds.

At this point you've already test-driven every layer (controllers, models, views, helpers, mailers, etc.) into existence, with only feature specs.

• Write model and helper specs to drive out detailed requirements which live entirely in those classes. For example, once you've written a single sad-path feature spec that establishes that entering one particular invalid attribute sends the user back to edit their form submission and displays a message, you can handle other invalid attributes entirely by writing more examples in that model's spec that test that model attributes are validated, and let the architecture that you've already test-driven propagate the errors back to the user.

  Note that although your feature specs already test the happy paths through model and helper methods, as soon as you start writing examples for a method for minor or error cases, you'll probably want to write the happy-path example or examples for that method too, so you can see the entire description of the method in one place, and so you can test the method fully just by running all its examples and not also have to run any feature specs.

You might not need some kinds of specs at all:

• Well-factored controller actions are short and have few or no conditionals, so you often won't need any controller specs at all. Write them only when needed, and stub out model, mailer, etc. behavior to keep them simple and fast.
• Similarly, views and mailers should have few or no conditionals (complex code should be refactored into helper and model methods), so you often won't need view or mailer specs at all.
• Your feature specs will have test-driven all the routes you need, so you probably won't need routing specs. I've only ever gotten use out of routing specs when I had to do a major refactor of routes, as when upgrading from one major version of Rails to the next.

As long as you always write a test before you write new code, you'll always have 100% line coverage.

Answer 2

That testing strategy sounds really comprehensive. If you had all of these tests in place you would have great test coverage. However it would take you longer to deliver your project. You would also not be agile as someone who is doing more limited testing. Testing has to suit the project. Don't over test. Over testing can cost time and money. Don't under test. Under testing can cost time and money.

There are right ways to do unit testing. There are right ways to do integration testing. The glove has to fit. If your application is largely front end facing then perhaps it's best to start with integration tests. If your writing a back end application or perhaps an API then unit tests maybe a better place to start. I think approaching with one style of testing and then expanding to different styles is a better start than to try and test every layer of your application.

Why not start with simple unit tests? They are easy to write. Write these tests and then track how many bugs you ship. Are you letting in too many bugs? Are you having a lot of regression issues? Are there bugs that are getting through to production that your suite is not picking up? If the answer is yes then maybe it's time to write some higher level tests. Remember the higher level a test is the more development cost you will have to pay.

If your not shipping bugs then you have no reason to write any more tests. Remember the end goal here. We want to ship bug free code. If we can write one test and one test alone that will ensure we are doing this then there is no reason to test any further.