[Reference] test: arbitrary changes to 4 source files and 6 test files#111076
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The git diff for the non-frontend file guard was comparing against HEAD (the synthetic merge commit) instead of HEAD^2 (the PR branch tip). This included base branch changes in the diff, causing false positives that unnecessarily forced full test runs. Made-with: Cursor
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Mar 30, 2026
_"Why run many unit test when few do trick?"_ – Kevin Malone, Senior Frontend Developer Changes the Frontend > Jest jobs to use Jest's [`--changedSince` option](https://jestjs.io/docs/cli#--changedsince) when possible. That has them only run test suites that are impacted by the changes in a PR based on the module dependency graph. Jest requires the commit history since the base commit, so this adds a second _"run only necessary Jest tests"_ flow in `frontend-optional.yml`. Specifically, that: 1. Increases the frontend-optional fetch-depth in PRs to `100`, which should get most PRs' commits pretty quickly 2. Tries to compute a `MERGE_BASE` using `git merge-base` * Note that this also clears `MERGE_BASE` if the PR touches any non-`static/` files. 3. If `MERGE_BASE` could be computed, passes it as a process env var to test scripts for use as Jest's `changedSince` * If `MERGE_BASE` couldn't be computed, the new _"run only necessary Jest tests"_ flow is skipped My plan (thanks to reviewer feedback) is to keep this running as a secondary, optional test flow on `master` for a couple weeks. If all seems well, we can remove the original _"run all Jest tests"_ logic and only run the _"run only necessary Jest tests"_ logic. The following PRs exercise different scales of changes: | PR | Source Files | Test Files | Interconnectivity | Ran Suites | / 1,881 suites | |---|---|---|---|---|---| | [#110624](#110624) | 0 | 1 | ⬜️ None | 1 | 0.05% | | [#111073](#111073) | 0 | 6 | ⬜️ None | 6 | 0.32% | | [#111122](#111122) | 0 | 100 | ⬜️ None | 100 | 5.3% | | [#111074](#111074) | 1 | 0 | 🟦 Low | 5 | 0.27% | | [#111075](#111075) | 4 | 0 | 🟦 Low | 7 | 0.37% | | [#111076](#111076) | 3 | 3 | 🟦 Low | 13 | 0.69% | | [#111110](#111110) | 20 | 20 | 🟦 Low | 74 | 3.9% | | [#111111](#111111) | 100 | 100 | 🟦 Low | 196 | 10.4% | | [#111119](#111119) | 1 | 1 | 🟨 Medium | 30 | 1.6% | | [#111628](#111628) | 3 | 3 | 🟨 Medium | 78 | 4.1% | | [#111629](#111629) | 10 | 10 | 🟨 Medium | 167 | 8.9% | | [#111633](#111633) | 25 | 25 | 🟨 Medium | 227 | 12.1% | | [#111652](#111652) | 100 | 100 | 🟨 Medium | 549 | 29.2% | | [#111115](#111115) | 3 | 3 | 🟧 High | 1,652 | 87.8% | | [#111083](#111083) | 20 | 20 | 🟧 High | 1,660 | 88.3% | | [#111086](#111086) | 100 | 100 | 🟧 High | 1,721 | 91.5% | | [#110568](#110568) | 0 | 0 | 🟥 Config (Full) | 1,881 | 100% | For low-connectivity changes (isolated components, feature-specific views), `--changedSince` provides pretty great savings: even 100 low-connectivity files only trigger ~10% of suites. Medium-connectivity files still scale pretty well, with 100 files hitting ~29%. High-connectivity files (widely-imported utils, core components) sadly trigger 85-90% of suites, which is inevitable given Sentry's highly connected module graph. Fixes ENG-7103
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Verifying #110568 works for: many sources and tests.