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Parallelizing directive

Webapp.io provides a utility to run tests in parallel - SPLIT 5 duplicates the entire VM 5 times at the point it executes. In practice this means that you can run tests in parallel without worrying about race conditions causing flaky tests.

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Rails: knapsack

See knapsack pro
  1. Install the gem
  2. Run KNAPSACK_GENERATE_REPORT=true bundle exec rspec spec on your local computer
  3. git add knapsack_rspec_report.json && git commit -m 'knapsack' && git push origin master
Your Layerfile will look something like this:
Layerfile
# install ruby, bundle install, etc

COPY . .
SPLIT 5
ENV CI_NODE_TOTAL=$SPLIT_NUM CI_NODE_INDEX=$SPLIT
RUN bundle exec knapsack:rspec

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Go: custom test runner

See this file for an example parallel test runner for go. The Layerfile from that example:
Layerfile
FROM ../base/Layerfile

COPY . .
SPLIT 5
RUN ./parallel-go-test.sh