From f6c4694636bf95ff2f3852c68edb5b32bf55c0a9 Mon Sep 17 00:00:00 2001
From: Lauren Tan <poteto@users.noreply.github.com>
Date: Tue, 6 Jan 2026 18:07:47 -0800
Subject: [PATCH 1/2] [ci] Increase DevTools test shards and bump timeout

[ci] Increase DevTools test shards and bump timeout

- Increase DevTools test shards from 3 to 5
- Bump timeout to 20s
---
 .github/workflows/runtime_build_and_test.yml              | 8 +++++---
 .../src/__tests__/profilerContext-test.js                 | 2 +-
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/.github/workflows/runtime_build_and_test.yml b/.github/workflows/runtime_build_and_test.yml
index 735ac6edb18..25282e8400a 100644
--- a/.github/workflows/runtime_build_and_test.yml
+++ b/.github/workflows/runtime_build_and_test.yml
@@ -454,9 +454,11 @@ jobs:
       fail-fast: false
       matrix:
         shard:
-          - 1/3
-          - 2/3
-          - 3/3
+          - 1/5
+          - 2/5
+          - 3/5
+          - 4/5
+          - 5/5
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
diff --git a/packages/react-devtools-shared/src/__tests__/profilerContext-test.js b/packages/react-devtools-shared/src/__tests__/profilerContext-test.js
index 7864f9703ea..a1e47defa2a 100644
--- a/packages/react-devtools-shared/src/__tests__/profilerContext-test.js
+++ b/packages/react-devtools-shared/src/__tests__/profilerContext-test.js
@@ -654,7 +654,7 @@ describe('ProfilerContext', () => {
     expect(store.profilerStore.isProfilingBasedOnUserInput).toBe(false);
 
     document.body.removeChild(profilerContainer);
-  });
+  }, 20000);
 
   it('should navigate between commits when the keyboard shortcut is pressed', async () => {
     const Parent = () => <Child />;

From 85773456e715cd68ca8b5080bed58f6175f482ba Mon Sep 17 00:00:00 2001
From: Lauren Tan <poteto@users.noreply.github.com>
Date: Tue, 6 Jan 2026 18:07:47 -0800
Subject: [PATCH 2/2] [ci] Add size-balanced test sequencer for better shard
 distribution

Jest's default test sequencer sorts alphabetically, causing large test files
(eg ReactDOMFloat-test.js at 9k lines, ReactHooksWithNoopRenderer-test.js at 4k
lines) to cluster in shard 3/5. This made shard 3/5 average 117s vs 77s for
other shards, a 52% slowdown. I'm using filesize as a rough proxy for number of tests.

This custom sequencer sorts tests by file size and distributes large files evenly across all shards
instead of clustering them together.
---
 scripts/jest/config.base.js           |  1 +
 scripts/jest/sizeBalancedSequencer.js | 28 +++++++++++++++++++++++++++
 2 files changed, 29 insertions(+)
 create mode 100644 scripts/jest/sizeBalancedSequencer.js

diff --git a/scripts/jest/config.base.js b/scripts/jest/config.base.js
index ba001e165ee..12b5fc45cd4 100644
--- a/scripts/jest/config.base.js
+++ b/scripts/jest/config.base.js
@@ -2,6 +2,7 @@
 
 module.exports = {
   globalSetup: require.resolve('./setupGlobal.js'),
+  testSequencer: require.resolve('./sizeBalancedSequencer.js'),
   modulePathIgnorePatterns: [
     '<rootDir>/scripts/rollup/shims/',
     '<rootDir>/scripts/bench/',
diff --git a/scripts/jest/sizeBalancedSequencer.js b/scripts/jest/sizeBalancedSequencer.js
new file mode 100644
index 00000000000..318cd136be4
--- /dev/null
+++ b/scripts/jest/sizeBalancedSequencer.js
@@ -0,0 +1,28 @@
+'use strict';
+
+const Sequencer = require('@jest/test-sequencer').default;
+const fs = require('fs');
+
+class SizeBalancedSequencer extends Sequencer {
+  shard(tests, {shardIndex, shardCount}) {
+    const shards = Array.from({length: shardCount}, () => ({
+      tests: [],
+      size: 0,
+    }));
+    const sorted = [...tests].sort(
+      (a, b) => fs.statSync(b.path).size - fs.statSync(a.path).size
+    );
+
+    for (let i = 0; i < sorted.length; i++) {
+      const test = sorted[i];
+      const size = fs.statSync(test.path).size;
+      const smallest = shards.reduce((min, s) => (s.size < min.size ? s : min));
+      smallest.tests.push(test);
+      smallest.size += size;
+    }
+
+    return shards[shardIndex - 1].tests;
+  }
+}
+
+module.exports = SizeBalancedSequencer;