// Find the top-N slowest test files in CI from a recent BuildKite run, optionally posting the results to a Slack channel as a formatted table. Use when asked to find slow CI tests, "what's making CI slow", or to post a slow-test report to Slack.
Implements JavaScript classes in C++ using JavaScriptCore. Use when creating new JS classes with C++ bindings, prototypes, or constructors.
Creates JavaScript classes using Bun's Zig bindings generator (.classes.ts). Use when implementing new JS APIs in Zig with JSC integration.
JSC GC reference for Bun. Use for use-after-free, JS object leaks, "collected too early", or when touching WriteBarrier, visitChildren, visitAdditionalChildren, JSRef, JSC::Strong/Weak, hasPendingActivity, ensureStillAlive, addOpaqueRoot, reportExtraMemoryAllocated, IsoSubspace, HeapAnalyzer, finalize.
Guides writing bundler tests using itBundled/expectBundled in test/bundler/. Use when creating or modifying bundler, transpiler, or code transformation tests.
Guides writing HMR/Dev Server tests in test/bake/. Use when creating or modifying dev server, hot reloading, or bundling tests.
Guides using bun.sys for system calls and file I/O in Zig. Use when implementing file operations instead of std.fs or std.posix.
| name | slowest-tests |
| description | Find the top-N slowest test files in CI from a recent BuildKite run, optionally posting the results to a Slack channel as a formatted table. Use when asked to find slow CI tests, "what's making CI slow", or to post a slow-test report to Slack. |
Args: [N] [#channel] — both optional. N defaults to 500. If #channel is omitted, just print the table and stop.
Run the script. With no build number it auto-picks the most recent finished build from a merged PR.
bun run ci:slowest # top 500 from a recent merged-PR build → TSV on stdout
bun run ci:slowest 47324 100 # specific build, top 100
bun run ci:slowest --json > /tmp/slow.json
The script (scripts/ci-slowest-tests.ts) does the heavy lifting:
test-bun jobs from bk build view <N>, skipping retried: true.raw_log_url directly with Authorization: Bearer $BUILDKITE_TOKEN. Do not use bk job log — it hangs indefinitely on some Windows/alpine jobs.$TMPDIR/bun-ci-logs-<build>/ so re-runs are instant._bk;t=<ms> ... --- [N/TOTAL] <file> group headers, normalising backslashes to / and stripping [attempt #N] retries.package.json / non-JS entries — those are setup steps, not tests.If the script can't find a build automatically (rare — it walks the last 10 merged PRs), pick one yourself: gh pr list --state merged --limit 10 --json number,headRefName, then bk build list --branch <headRefName> and pass the first build with a finished_at. Merged-PR builds usually report state: failed because of flaky tests — that's fine, the timing data is still valid.
slack_send_message does NOT support markdown tables — its markdown→blocks converter rejects | a | b | syntax with invalid_blocks. Don't use Canvases either; they render tables but the MCP proxy 502s above ~10 KB and the result is clunky.
Procedure:
Look up the channel ID with slack_search_channels (the user gives a name, you need the C… ID).
Write the full N-row markdown table to ~/code/tmp/top<N>-slow-tests.md, then upload it as a secret gist: gh gist create <file> --desc "Bun CI: top N slowest test files (build #<num>)". (The Slack MCP has no file-upload tool; secret gist is the agreed fallback. Do not ask the user to attach anything manually.)
Post the main message: header (build link + gist link, "Rest in thread.") followed by the top 20 bullets. Row format:
• 325s `test/js/bun/cron/in-process-cron.test.ts` 🐧 x64-baseline
• 96s `test/js/bun/http/serve-body-leak.test.ts` 🐧 x64-asan
test/ prefix and extension — do not strip anythingx64-asan, aarch64, x64-baseline — do not abbreviate)Reply in-thread (thread_ts = the main message) with rows 21–N in the same bullet format, packed into chunks under 4800 chars each (~70 rows per chunk). Post chunks sequentially so they stay ordered.