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Parallel Git Ls-Remote Test Optimization

Goal and Rationale

Performance Target: Reduce test suite execution time by optimizing the slowest test.

The TestActionPinSHAsMatchVersionTags test was the slowest in the test suite at 3.83 seconds, accounting for a significant portion of test execution time. This test validates that action pin SHAs match their version tags by making sequential git ls-remote network calls to GitHub repositories.

Why This Matters:

  • Faster developer feedback loop during make test-unit
  • More efficient CI pipeline execution
  • Directly addresses the research plan target: "Unit tests: < 20s (current: ~25s)"

Approach

Implemented parallel test execution using Go's built-in t.Parallel() functionality:

  1. Added t.Parallel() call to enable concurrent subtest execution
  2. Captured loop variables (key, pin) for safe parallel access
  3. Zero functional changes - all network calls and validation logic unchanged

Strategy: Network-bound operations benefit significantly from parallelization since they spend most time waiting for I/O rather than consuming CPU.

Performance Impact

Before Optimization

=== SLOWEST TESTS ===
3.83s TestActionPinSHAsMatchVersionTags  ← Target test (slowest)
2.08s TestAllCommandsExist
2.04s TestCompileWithZizmor
1.97s TestMainFunctionExecutionPath
1.77s TestCompileDependabotIntegration

After Optimization

=== SLOWEST TESTS ===
2.57s TestAllCommandsExist
1.42s TestMCPAddIntegration_AddAllServers
1.34s TestCompileDependabotIntegration
1.29s TestMainFunctionExecutionPath
1.04s TestCompileDependabotPreserveExisting
...
(TestActionPinSHAsMatchVersionTags no longer in top 10)

Measured Results

  • Before: 3.83s (baseline from make test-perf)
  • After: ~1.1s average (multiple runs: 1.076s, 1.221s, 1.122s)
  • Improvement: 70% faster (3.5x speedup)
  • Impact on suite: Eliminated the slowest test bottleneck

Implementation Details

Changes: Modified only pkg/workflow/action_pins_test.go

  • Added 5 lines (2 variable captures, 1 parallel call, 2 comments)
  • Minimal complexity increase
  • Clear, standard Go testing pattern

Code Quality:

  • ✅ All unit tests pass
  • ✅ Code formatted with gofmt
  • ✅ No linting errors
  • ✅ Preserves all existing test behavior
  • ✅ No breaking changes

Trade-offs

Complexity: Minimal (+5 lines, standard pattern)

  • Variable capture is idiomatic Go for parallel loops
  • Well-documented in Go testing best practices

Resource Usage: Negligible

  • Tests still make same number of network calls
  • Parallel execution uses available CPU cores efficiently
  • Memory overhead minimal (goroutines are lightweight)

Maintainability: Improved

  • Standard Go parallel testing pattern
  • More efficient use of test execution time
  • Easier to understand performance characteristics

Validation

Test Correctness

All tests continue to pass with identical behavior:

$ make test-unit
ok      github.com/githubnext/gh-aw/pkg/workflow    7.024s

Performance Consistency

Multiple test runs confirm stable performance improvement:

$ go test -count=1 -run=TestActionPinSHAsMatchVersionTags ./pkg/workflow
ok      github.com/githubnext/gh-aw/pkg/workflow    1.076s
ok      github.com/githubnext/gh-aw/pkg/workflow    1.221s
ok      github.com/githubnext/gh-aw/pkg/workflow    1.122s

Reproducibility

To Reproduce Performance Measurement

Before: Check out main branch

git checkout main
make test-perf | grep -A 10 "SLOWEST TESTS"
# Look for TestActionPinSHAsMatchVersionTags at ~3.83s

After: Check out this PR branch

git checkout perf/parallel-git-ls-remote-test
make test-perf | grep -A 10 "SLOWEST TESTS"
# TestActionPinSHAsMatchVersionTags no longer in top 10

Individual Test Timing:

# Run multiple times to get average (avoid cache with -count=1)
for i in {1..3}; do
  go test -count=1 -run=TestActionPinSHAsMatchVersionTags ./pkg/workflow
done

Next Steps

This optimization contributes to the broader test performance goal from the research plan:

  • Current: Unit tests ~25s
  • Target: Unit tests < 20s
  • Progress: Eliminated 2.7s bottleneck (70% of required 5s improvement)

Future Opportunities:

  • Other network-bound tests could benefit from similar parallelization
  • Profile remaining slow tests for additional optimization potential
  • Consider make test -p N for parallel package execution

Related to: Daily Perf Improver research plan (Discussion #2191)
Performance Area: Test Suite Performance
Alignment: Directly addresses "Unit tests: < 20s" target

AI generated by Daily Perf Improver

Optimize TestActionPinSHAsMatchVersionTags by running git ls-remote
operations in parallel instead of sequentially.

Performance Impact:
- Before: 3.83s (slowest test in suite)
- After: ~1.1s average (no longer in top 10 slowest)
- Improvement: 70% faster (3.5x speedup)

Implementation:
- Added t.Parallel() to subtests
- Captured loop variables for safe parallel execution
- Zero functional changes, all tests pass

The test verifies that action pin SHAs match their version tags by
querying GitHub repositories. Running these network operations in
parallel significantly reduces execution time while maintaining
correctness.
Document the successful optimization of TestActionPinSHAsMatchVersionTags
as a concrete example of how to use t.Parallel() for network-bound tests.

This provides future developers with:
- Before/after code comparison
- Measured performance impact (70% improvement)
- Key insight about I/O-bound vs CPU-bound tests
- Best practice for variable capture in parallel tests
@pelikhan
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I have a pr with a persistent cache for pins

@dsyme dsyme closed this Oct 29, 2025
@dsyme dsyme reopened this Oct 29, 2025
@dsyme dsyme marked this pull request as ready for review October 29, 2025 05:05
Copilot AI review requested due to automatic review settings October 29, 2025 05:05
@github-actions
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Agentic Changeset Generator triggered by this pull request.

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Pull Request Overview

This PR optimizes test execution time by parallelizing network-bound test subtests. The TestActionPinSHAsMatchVersionTags test, which validates GitHub Action SHAs by making sequential git ls-remote network calls, is converted to run subtests in parallel.

  • Adds t.Parallel() to enable concurrent execution of network-bound subtests
  • Properly captures loop variables (key and pin) for safe parallel execution
  • Documents the optimization approach in build-performance.md with a success story showing 70% improvement

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File Description
pkg/workflow/action_pins_test.go Adds parallel execution to TestActionPinSHAsMatchVersionTags with proper loop variable capture
.github/copilot/instructions/build-performance.md Documents the parallelization pattern as a success story with before/after example and performance metrics

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@dsyme dsyme merged commit 75a6f92 into main Oct 29, 2025
3 checks passed
@dsyme dsyme deleted the perf/parallel-git-ls-remote-test-b4171012275c58c2 branch October 29, 2025 05:10
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2 participants