debian-mirror-gitlab/doc/ci/testing/fail_fast_testing.md

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Fail Fast Testing (PREMIUM)

Introduced in GitLab 13.1.

For applications that use RSpec for running tests, we've introduced the Verify/Failfast template to run subsets of your test suite, based on the changes in your merge request.

The template uses the test_file_finder (tff) gem that accepts a list of files as input, and returns a list of spec (test) files that it believes to be relevant to the input files.

tff is designed for Ruby on Rails projects, so the Verify/FailFast template is configured to run when changes to Ruby files are detected. By default, it runs in the .pre stage of a GitLab CI/CD pipeline, before all other stages.

Example use case

Fail fast testing is useful when adding new functionality to a project and adding new automated tests.

Your project could have hundreds of thousands of tests that take a long time to complete. You may expect a new test to pass, but you have to wait for all the tests to complete to verify it. This could take an hour or more, even when using parallelization.

Fail fast testing gives you a faster feedback loop from the pipeline. It lets you know quickly that the new tests are passing and the new functionality did not break other tests.

Prerequisites

This template requires:

• A project built in Rails that uses RSpec for testing.
• CI/CD configured to:
  • Use a Docker image with Ruby available.
  • Use Merge request pipelines
• Merged results pipelines enabled in the project settings.
• A Docker image with Ruby available. The template uses image: ruby:2.6 by default, but you can override this.

Configuring Fast RSpec Failure

We use the following plain RSpec configuration as a starting point. It installs all the project gems and executes rspec, on merge request pipelines only.

rspec-complete:
  stage: test
  rules:
    - if: $CI_PIPELINE_SOURCE == "merge_request_event"
  script:
    - bundle install
    - bundle exec rspec

To run the most relevant specs first instead of the whole suite, include the template by adding the following to your CI/CD configuration:

include:
  - template: Verify/FailFast.gitlab-ci.yml

To customize the job, specific options may be set to override the template. For example, to override the default Docker image:

include:
  - template: Verify/FailFast.gitlab-ci.yml

rspec-rails-modified-path-specs:
  image: custom-docker-image-with-ruby

Example test loads

For illustrative purposes, let's say our Rails app spec suite consists of 100 specs per model for ten models.

If no Ruby files are changed:

• rspec-rails-modified-paths-specs does not run any tests.
• rspec-complete runs the full suite of 1000 tests.

If one Ruby model is changed, for example app/models/example.rb, then rspec-rails-modified-paths-specs runs the 100 tests for example.rb:

• If all of these 100 tests pass, then the full rspec-complete suite of 1000 tests is allowed to run.
• If any of these 100 tests fail, they fail quickly, and rspec-complete does not run any tests.

The final case saves resources and time as the full 1000 test suite does not run.