A unit test is about testing a single function/method in isolation with all of its possible outputs.
A functional test is about testing a single functionality, which can span multiple methods and a controller.
Other common terms in Rails are "model tests", "controller tests" and others.
You can find model tests in
spec/models, controller tests in
spec/controllers and additional functional tests in various directories within the
You can run all models tests, for example, with:
bundle exec rspec spec/models
To run an individual file you can use for example:
bundle exec rspec spec/models/user_spec.rb
To run a specific test case you can use for example:
bundle exec rspec spec/models/user_spec.rb:10
10 is the line number of the test case you want to execute.
You can read the official guide Testing Rails Applications to learn more.