Parallelize collection tests into 4 shards

[kenyonj]

Summary

• Split collection tests across 4 parallel GitHub Actions matrix jobs
• Each shard tests ~25 collections instead of all ~100
• Reduces wall-clock time for collection testing by ~4x

Changes

• test/collections_test_helper.rb: Add shard_collections function that uses modular arithmetic on alphabetically sorted collections. Modified collections to apply sharding when COLLECTION_SHARD and COLLECTION_TOTAL_SHARDS env vars are set
• .github/workflows/test.yml: Replace single collections matrix entry with 4 sharded entries (shard 0-3). Pass shard env vars to the test step

How sharding works

Collections are sorted alphabetically for deterministic assignment. Each collection is assigned to shard index % total_shards. For example with 4 shards:

• Shard 0: collections at indices 0, 4, 8, 12, ...
• Shard 1: collections at indices 1, 5, 9, 13, ...
• etc.

Notes

• topics and all jobs are unaffected
• The shard count can be adjusted by modifying the matrix entries
• When shard env vars are not set (e.g., local development), all collections are tested

[Copilot]

Pull request overview

This PR parallelizes collection tests across 4 shards to reduce wall-clock time by approximately 4x. The sharding is implemented using modular arithmetic on alphabetically sorted collections, where each of the 4 GitHub Actions matrix jobs tests roughly 25% of the ~100 collections.

Changes:

• Added sharding logic to split collection tests across parallel jobs
• Modified GitHub Actions workflow to create 4 separate collection test jobs
• Implemented deterministic shard assignment using alphabetical sorting and modulo operation

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
test/collections_test_helper.rb	Added shard_collections function to filter collections based on shard environment variables
.github/workflows/test.yml	Replaced single collections matrix entry with 4 sharded entries and passed shard environment variables

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[Copilot]

The condition shard && total_shards && total_shards > 1 will fail when shard is 0 because 0 is falsy in Ruby. This means shard 0 (the first shard in the matrix) will incorrectly test all collections instead of just every 4th collection starting at index 0. The condition should check for nil explicitly instead: !shard.nil? && !total_shards.nil? && total_shards > 1.

[kenyonj]

Fixed in 198d465 — switched to explicit nil checks: !shard.nil? && !total_shards.nil? && total_shards > 1. This also avoids the falsy-zero bug for shard 0. Thanks for the catch!