Run tests in parallel

[harigopal]

@pupilfirst/developers This adds the parallel_tests gem to run Rspec tests in parallel with multiple databases. On my 8-core laptop, this runs with 16 processes by default and finishes all tests in approx 2:50 (m:ss). Manually setting the number of processes to 8 reduces memory pressure somewhat, and still finishes in 3:10. So it seems hyper-threading doesn't help too much.

To run tests in parallel on this branch, do:

# Create the parallel databases (equal to number of logical processors)
bundle exec rails parallel:create

# Load schema into all of these databases
bundle exec rails parallel:prepare

# Run the tests. I had to pass RAILS_ENV=tests to get this to work.
RAILS_ENV=test bundle exec rails parallel:spec

# Or to limit the number of processes to 8...
RAILS_ENV=test bundle exec "rails parallel:spec[8]"

A few specs are failing for me (2 to 3).

Running failing specs using bundle exec rspec --only-failures is also resulting in failures, so this needs looking into.

Merge Checklist

• Add specs that demonstrate bug / test a new feature.
• Check if route, query, or mutation authorization looks correct.
  • Add tests for authorization, if required.
• Ensure that UI text is kept in I18n files.
• Update developer and product docs, where applicable.
• Prep screenshot or demo video for changelog entry, and attach it to issue.
• Check if new tables or columns that have been added need to be handled in the following services:
  • Users::DeleteAccountService
  • Courses::CloneService
  • Courses::DeleteService
  • Courses::DemoContentService
  • Levels::CloneService
  • Schools::DeleteService
• Check if changes in packaged components have been published to npm.
• Add development seeds for new tables.
• If the updates involve Graph mutations ensure that the files are migrated to the new approach without a mutator.
• If the updates involve adding a new table ensure that rate limiting is added and documented in the docs/developers/rate_limiting.md file.