What is Better Specs Better Specs is a collection of best practices developers learned while testing apps that you can use to improve your coding skills, or simply for inspiration. Better Specs came to life at Lelylan (open source IoT cloud platform) and checking out its test suite may be of inspiration. Better Specs focus on Rails testing, but our goal is to create testing guidelines covering most languages and frameworks out there (e.g. Scala, Elixir, React). If you want to add your favourite language testing guidelines open an issue.

Describe Your Methods Be clear about what method you are describing. For instance, use the Ruby documentation convention of . (or :: ) when referring to a class method's name and # when referring to an instance method's name. bad describe 'the authenticate method for User' do describe 'if the user is an admin' do good describe '.authenticate' do describe '#admin?' do Discuss this guideline →

Use contexts Contexts are a powerful method to make your tests clear and well organized (they keep tests easy to read). When describing a context, start its description with 'when', 'with' or 'without'. bad it 'has 200 status code if logged in' do expect ( response ). to respond_with 200 end it 'has 401 status code if not logged in' do expect ( response ). to respond_with 401 end good context 'when logged in' do it { is_expected . to respond_with 200 } end context 'when logged out' do it { is_expected . to respond_with 401 } end Discuss this guideline →

Keep your description short A spec description should never be longer than 40 characters. If this happens you should split it using a context. bad it 'has 422 status code if an unexpected params will be added' do good context 'when not valid' do it { is_expected . to respond_with 422 } end In the example we removed the description related to the status code, which has been replaced by the expectation is_expected . If you run this test typing rspec filename you will obtain a readable output. Formatted output when not valid it should respond with 422 Discuss this guideline →

Single expectation test The 'one expectation' tip is more broadly expressed as 'each test should make only one assertion'. This helps you on finding possible errors, going directly to the failing test, and to make your code readable. In isolated unit specs, you want each example to specify one (and only one) behavior. Multiple expectations in the same example are a signal that you may be specifying multiple behaviors. good (isolated) it { is_expected . to respond_with_content_type ( :json ) } it { is_expected . to assign_to ( :resource ) } Anyway, in tests that are not isolated (e.g. ones that integrate with a DB, an external webservice, or end-to-end-tests), you take a massive performance hit to do the same setup over and over again, just to set a different expectation in each test. In these sorts of slower tests, I think it's fine to specify more than one isolated behavior. good (not isolated) it 'creates a resource' do expect ( response ). to respond_with_content_type ( :json ) expect ( response ). to assign_to ( :resource ) end Discuss this guideline →

Test all possible cases Testing is a good practice, but if you do not test the edge cases, it will not be useful. Test valid, edge and invalid case. For example, consider the following action. Destroy Action before_action :find_owned_resources before_action :find_resource def destroy render 'show' @consumption . destroy end The error I usually see lies in testing only whether the resource has been removed. But there are at least two edge cases: when the resource is not found and when it's not owned. As a rule of thumb think of all the possible inputs and test them. bad it 'shows the resource' good describe '#destroy' do context 'when resource is found' do it 'responds with 200' it 'shows the resource' end context 'when resource is not found' do it 'responds with 404' end context 'when resource is not owned' do it 'responds with 404' end end Discuss this guideline →

Expect vs Should syntax On new projects always use the expect syntax. bad it 'creates a resource' do response . should respond_with_content_type ( :json ) end good it 'creates a resource' do expect ( response ). to respond_with_content_type ( :json ) end Configure the RSpec to only accept the new syntax on new projects, to avoid having the 2 syntax all over the place. good # spec_helper.rb RSpec . configure do | config | # ... config . expect_with :rspec do | c | c . syntax = :expect end end On one line expectations or with implicit subject we should use is_expected.to . bad context 'when not valid' do it { should respond_with 422 } end good context 'when not valid' do it { is_expected . to respond_with 422 } end On old projects you can use the transpec to convert them to the new syntax. More about the new RSpec expectation syntax can be found here and here. Discuss this guideline →

Use subject If you have several tests related to the same subject use subject{} to DRY them up. bad it { expect ( assigns ( 'message' )). to match /it was born in Belville/ } good subject { assigns ( 'message' ) } it { is_expected . to match /it was born in Billville/ } RSpec has also the ability to use a named subject (learn more about rspec subject). good subject ( :hero ) { Hero . first } it "carries a sword" do expect ( hero . equipment ). to include "sword" end Discuss this guideline →

Use let and let! When you have to assign a variable instead of using a before block to create an instance variable, use let . Using let the variable lazy loads only when it is used the first time in the test and get cached until that specific test is finished. A really good and deep description of what let does can be found in this stackoverflow answer. bad describe '#type_id' do before { @resource = FactoryBot . create :device } before { @type = Type . find @resource . type_id } it 'sets the type_id field' do expect ( @resource . type_id ). to equal ( @type . id ) end end good describe '#type_id' do let ( :resource ) { FactoryBot . create :device } let ( :type ) { Type . find resource . type_id } it 'sets the type_id field' do expect ( resource . type_id ). to equal ( type . id ) end end Use let to initialize actions that are lazy loaded to test your specs. good context 'when updates a not existing property value' do let ( :properties ) { { id: Settings . resource_id , value: 'on' } } def update resource . properties = properties end it 'raises a not found error' do expect { update }. to raise_error Mongoid :: Errors :: DocumentNotFound end end Use let! if you want to define the variable when the block is defined. This can be useful to populate your database to test queries or scopes. Here an example of what let actually is (learn more about rspec let). Explenation # this use of let let ( :foo ) { Foo . new } # is very nearly equivalent to this: def foo @foo ||= Foo . new end Discuss this guideline →

Mock or not to mock As general rule do not (over)use mocks and test real behavior when possible, as testing real cases is useful when validating your application flow. good # simulate a not found resource context "when not found" do before do allow ( Resource ). to receive ( :where ). with ( created_from: params [ :id ]) . and_return ( false ) end it { is_expected . to respond_with 404 } end Mocking makes your specs faster but they are difficult to use. You need to understand them well to use them well. Read this article to learn more about mocks. Discuss this guideline →

Create only the data you need If you have ever worked in a medium size project (but also in small ones), test suites can be heavy to run. To solve this problem, it's important not to load more data than needed. Also, if you think you need dozens of records, you are probably wrong. good describe "User" do describe ".top" do before { FactoryBot . create_list ( :user , 3 ) } it { expect ( User . top ( 2 )). to have ( 2 ). item } end end Discuss this guideline →

Use factories and not fixtures This is an old topic, but it's still good to remember it. Do not use fixtures because they are difficult to control, use factories instead. Use them to reduce the verbosity on creating new data (learn about Factory Bot). bad user = User . create ( name: 'Genoveffa' , surname: 'Piccolina' , city: 'Billyville' , birth: '17 Agoust 1982' , active: true ) good user = FactoryBot . create :user One important note. When talking about unit tests the best practice would be to use neither fixtures or factories. Put as much of your domain logic in libraries that can be tested without needing complex, time consuming setup with either factories or fixtures. Read more in this article. Discuss this guideline →

Easy to read matchers Use readable matchers and double check the available rspec matchers. bad lambda { model . save! }. to raise_error Mongoid :: Errors :: DocumentNotFound good expect { model . save! }. to raise_error Mongoid :: Errors :: DocumentNotFound Discuss this guideline →

Shared Examples Making tests is great and you get more confident day after day. But in the end you will start to see code duplication coming up everywhere. Use shared examples to DRY your test suite up. bad describe 'GET /devices' do let! ( :resource ) { FactoryBot . create :device , created_from: user . id } let! ( :uri ) { '/devices' } context 'when shows all resources' do let! ( :not_owned ) { FactoryBot . create factory } it 'shows all owned resources' do page . driver . get uri expect ( page . status_code ). to be ( 200 ) contains_owned_resource resource does_not_contain_resource not_owned end end describe '?start=:uri' do it 'shows the next page' do page . driver . get uri , start: resource . uri expect ( page . status_code ). to be ( 200 ) contains_resource resources . first expect ( page ). to_not have_content resource . id . to_s end end end good describe 'GET /devices' do let! ( :resource ) { FactoryBot . create :device , created_from: user . id } let! ( :uri ) { '/devices' } it_behaves_like 'a listable resource' it_behaves_like 'a paginable resource' it_behaves_like 'a searchable resource' it_behaves_like 'a filterable list' end In our experience, shared examples are used mainly for controllers. Since models are pretty different from each other, they (usually) do not share much logic. Learn more about rspec shared examples. Discuss this guideline →

Test what you see Deeply test your models and your application behaviour (integration tests). Do not add useless complexity testing controllers. When I first started testing my apps I was testing controllers, now I don't. Now I only create integration tests using RSpec and Capybara. Why? Because I believe that you should test what you see and because testing controllers is an extra step you wont usually need. You'll find out that most of your tests go into the models and that integration tests can be easily grouped into shared examples, building a clear and readable test suite. This is an open debate in the Ruby community and both sides have good arguments supporting their idea. People supporting the need of testing controllers will tell you that your integration tests don't cover all use cases and that they are slow. Both are wrong. You can easily cover all use cases (why shouldn't you?) and you can run single file specs using automated tools like Guard. In this way you will run only the specs you need to test blazing fast without stopping your flow. Discuss this guideline →

Don't use should Do not use should when describing your tests. Use the third person in the present tense. Even better start using the new expectation syntax. bad it 'should not change timings' do consumption . occur_at . should == valid . occur_at end good it 'does not change timings' do expect ( consumption . occur_at ). to equal ( valid . occur_at ) end See the should_not gem for a way to enforce this in RSpec and the should_clean gem for a way to clean up existing RSpec examples that begin with 'should.' Discuss this guideline →

Automatic tests with guard Running all the test suite every time you change your app can be cumbersome. It takes a lot of time and it can break your flow. With Guard you can automate your test suite running only the tests related to the updated spec, model, controller or file you are working at. good bundle exec guard Here you can see a sample Guardfile with some basic reloading rules. good guard 'rspec' , cli: '--drb --format Fuubar --color' , version: 2 do # run every updated spec file watch ( %r{^spec/.+_spec \. rb$} ) # run the lib specs when a file in lib/ changes watch ( %r{^lib/(.+) \. rb$} ) { | m | "spec/lib/ #{ m [ 1 ] } _spec.rb" } # run the model specs related to the changed model watch ( %r{^app/(.+) \. rb$} ) { | m | "spec/ #{ m [ 1 ] } _spec.rb" } # run the view specs related to the changed view watch ( %r{^app/(.*)( \. erb| \. haml)$} ) { | m | "spec/ #{ m [ 1 ] }#{ m [ 2 ] } _spec.rb" } # run the integration specs related to the changed controller watch ( %r{^app/controllers/(.+) \. rb} ) { | m | "spec/requests/ #{ m [ 1 ] } _spec.rb" } # run all integration tests when application controller change watch ( 'app/controllers/application_controller.rb' ) { "spec/requests" } end Guard is a fine tool but as usual it doesn't fit all of your needs. Sometimes your TDD workflow works best with a keybinding that makes it easy to run just the examples you want when you want to. Then, you can use a rake task to run the entire suite before pushing code. Find an example vim keybinding here and learn more about guard-rspec. Discuss this guideline →

Faster tests (preloading Rails) When running a test on Rails the whole Rails app is loaded. This can take time and it can break your development flow. To solve this problem use solutions like Zeus, Spin or Spork. Those solutions will preload all libraries you (usually) do not change and reload controllers, models, view, factories and all the files you change most often. Here you can find a spec helper and a Guardfile configuration based on Spork. With this configuration you will reload the whole app if a preloaded file (like initializers) change and you will run the single tests really, really fast. The drawback of using Spork is that it aggressively monkey-patches your code and you could lose some hours trying to understand why a file is not reloaded. If you have some code examples using Spin or any other solution let us know. Here you can find a Guardfile configuration for using Zeus. The spec_helper does not need to be modified, however, you will have to run `zeus start` in a console to start the zeus server before running your tests. Although Zeus takes a less aggressive approach than Spork, one major drawback is the fairly strict usage requirements; Ruby 1.9.3+ (recommended using backported GC from Ruby 2.0) as well as an operating system that supports FSEvents or inotify is required. Many criticisms are moved to those solutions. Those libraries are a band aid on a problem that is better solved through better design, and being intentional about only loading the dependencies that you need. Learn more reading the related discussion. Discuss this guideline →

Stubbing HTTP requests Sometimes you need to access external services. In these cases you can't rely on the real service but you should stub it with solutions like webmock. good context "with unauthorized access" do let ( :uri ) { 'http://api.lelylan.com/types' } before { stub_request ( :get , uri ). to_return ( status: 401 , body: fixture ( '401.json' )) } it "gets a not authorized notification" do page . driver . get uri expect ( page ). to have_content 'Access denied' end end Learn more about webmock and VCR. Here a nice presentation explaining how to mix them together. Discuss this guideline →

Useful formatter Use a formatter that can give you useful information about the test suite. I personally find fuubar really nice. To make it work add the gem and set fuubar as default formatter in your Guardfile. good # Gemfile group :development , :test do gem 'fuubar' # .rspec configuration file -- drb -- format Fuubar -- color Learn more about fuubar. Discuss this guideline →