spectracer (noun): something exhibited to view as unusual, notable, or entertaining

Spectracer is a Ruby gem that intelligently determines which specs to run based on the files you've changed. By tracing dependencies during test execution, Spectracer builds a map of which source files are used by which specs, then uses this data to run only the relevant tests.

• Dependency tracing - Automatically tracks which files each spec depends on
• Smart test selection - Only runs specs affected by your changes
• CI integration - Built for Buildkite with parallel job support
• Framework support - Works with both RSpec and Minitest
• Rails compatible - Includes Railtie for automatic setup

Add Spectracer to your Gemfile:

group :development, :test do
  gem "spectracer", github: "mitchbne/spectracer", branch: "main"
end

Then run:

bundle install
bundle exec rake spectracer:install

This creates a .spectracer.yml configuration file in your project root.

Spectracer operates in three phases:

Run your full test suite with tracing enabled:

WITH_SPECTRACER_TRACING=true bundle exec rspec

This uses Ruby's TracePoint to record which files each spec touches, outputting a gzipped JSON file mapping specs to their dependencies.

After running specs across parallel jobs, collect all tracing artifacts:

bundle exec rake spectracer:collect_dependencies

This combines individual trace files into a single inverse dependency map: for each source file, which specs depend on it.

When running tests on a branch, determine which specs to run:

SPECS=$(bundle exec rake spectracer:spec_determiner)
bundle exec rspec $SPECS

Create a .spectracer.yml file in your project root:

defaults:
  all_specs: "spec/**/*_spec.rb"
  no_specs: ""

on_empty_spec_set: "{{all_specs}}"

globs_matcher:
  "Gemfile": "{{all_specs}}"
  "Gemfile.lock": "{{all_specs}}"
  "db/schema.rb": "spec/models/**/*_spec.rb"
  "config/routes.rb": "spec/routing/**/*_spec.rb"
  "app/views/**/*": "spec/views/**/*_spec.rb,spec/features/**/*_spec.rb"

Example pipeline.yml:

steps:
  # Step 1: Run full suite with tracing (weekly/nightly)
  - label: ":rspec: Full Suite with Tracing"
    command: |
      WITH_SPECTRACER_TRACING=true bundle exec rspec --format progress
    artifact_paths:
      - "tmp/spectracer/**/*"
    branches: main

  # Step 2: Collect dependencies
  - label: ":package: Collect Dependencies"
    command: |
      buildkite-agent artifact download "tmp/spectracer/**/*" .
      bundle exec rake spectracer:collect_dependencies
    artifact_paths:
      - "tmp/spectracer/dependencies.json.gz"
    depends_on: "full-suite"

  # Step 3: Run affected specs on feature branches
  - label: ":rspec: Affected Specs"
    command: |
      buildkite-agent artifact download "tmp/spectracer/dependencies.json.gz" .
      SPECS=$(bundle exec rake spectracer:spec_determiner)
      bundle exec rspec $SPECS
    branches: "!main"

Spectracer automatically configures RSpec when required. No additional setup needed:

# Gemfile
gem "spectracer"

# That's it! Tracing is enabled via WITH_SPECTRACER_TRACING=true

Spectracer also supports Minitest:

# test/test_helper.rb
require "spectracer"

# Tracing is automatically enabled when WITH_SPECTRACER_TRACING=true

Enable debug logging to see what Spectracer is doing:

WITH_SPECTRACER_DEBUG=true bundle exec rake spectracer:spec_determiner

After checking out the repo:

bin/setup                    # Install dependencies
bundle exec rake             # Run tests + linting
bundle exec rspec            # Run tests only
bundle exec standardrb       # Run linting only

See docs/architecture.md for detailed architecture documentation.

Bug reports and pull requests are welcome on GitHub at https://github.com/mitchbne/spectracer.

The gem is available as open source under the terms of the MIT License.