Parallelize rspec tests

[akarki2005]

Proposed Changes

Adds the parallel_tests gem to run RSpec tests in parallel, reducing CI test suite runtime. Each parallel worker gets its own isolated test database using the TEST_ENV_NUMBER environment variable. System tests continue to run sequentially as they require a browser.

Type of Change

(Write an X or a brief description next to the type or types that best describe your changes.)

Type	Applies?
🚨 Breaking change (fix or feature that would cause existing functionality to change)
✨ New feature (non-breaking change that adds functionality)
🐛 Bug fix (non-breaking change that fixes an issue)
🎨 User interface change (change to user interface; provide screenshots)
♻️ Refactoring (internal change to codebase, without changing functionality)
🚦 Test update (change that only adds or modifies tests)
📦 Dependency update (change that updates a dependency)
🔧 Internal (change that only affects developers or continuous integration)	X

Checklist

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Before opening your pull request:

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• [N/A] I have added tests for my changes, if applicable.
  • This is required for all bug fixes and new features.
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Questions and Comments

[akarki2005]

Hi @david-yz-liu, I'm seeing that the CI run is failing due to the parallel_tests gem not getting installed properly - I made a commit to try and address this, but I think the bundle cache is stale, and I'm unable to change Gemfile.lock to re-trigger it. Are you able to clear the Actions cache for my PR? Thanks :)

[david-yz-liu]

@akarki2005 I removed the gem cache and re-ran the tests. It looks like the gem installed correctly, but there's an issue with bundler using parallel_tests. See my comments for a suggested fix.

[david-yz-liu]

Use rails (not rake) as the task runner; this is the more modern convention

[david-yz-liu]

Use rails parallel:spec rather than parallel_tests. I suspect this is causing the issue with parallel_tests not being found in the GitHub Actions workflow.

[david-yz-liu]

This dependency should not be changed