tests(smokehouse): add flag for test sharding

.github/workflows/smoke.yml

@@ -13,15 +13,16 @@ jobs:
     strategy:
       matrix:
         chrome-channel: ['stable', 'ToT']
-        smoke-test-invert: [false, true]
+        smoke-test-shard: [1, 2]
       # e.g. if set 1 fails, continue with set 2 anyway
       fail-fast: false
     runs-on: ubuntu-latest
     env:
-      # The smokehouse tests run by job `test set 1`. `test set 2` will run the rest.
-      SMOKE_BATCH_1: a11y oopif pwa dbw redirects errors offline
-    # Job named e.g. "Chrome stable, test set 1".
-    name: Chrome ${{ matrix.chrome-channel }}, batch ${{ matrix.smoke-test-invert == false && '1' || '2' }}
+      # The total number of shards. Set dynamically when length of single matrix variable is
+      # computable. See https://github.community/t/get-length-of-strategy-matrix-or-get-all-matrix-options/18342
+      SHARD_TOTAL: 2
+    # Job named e.g. "Chrome stable, batch 1".
+    name: Chrome ${{ matrix.chrome-channel }}, batch ${{ matrix.smoke-test-shard }}
 
     steps:
     - name: git clone
@@ -52,7 +53,7 @@ jobs:
     - run: sudo apt-get install xvfb
     - name: Run smoke tests
       run: |
-        xvfb-run --auto-servernum yarn c8 yarn smoke --debug -j=1 --retries=2 --invert-match ${{ matrix.smoke-test-invert }} $SMOKE_BATCH_1
+        xvfb-run --auto-servernum yarn c8 yarn smoke --debug -j=1 --retries=2 --shard=${{ matrix.smoke-test-shard }}/$SHARD_TOTAL
         yarn c8 report --reporter text-lcov > smoke-coverage.lcov
 
     - name: Upload test coverage to Codecov

lighthouse-cli/test/smokehouse/frontends/smokehouse-bin.js

@@ -13,6 +13,7 @@
 
 /* eslint-disable no-console */
 
+import {strict as assert} from 'assert';
 import path from 'path';
 import fs from 'fs';
 import url from 'url';
@@ -79,6 +80,52 @@ function getDefinitionsToRun(allTestDefns, requestedIds, {invertMatch}) {
   return smokes;
 }
 
+/**
+ * Parses the cli `shardArg` flag into `shardNumber/shardTotal`. Splits
+ * `testDefns` into `shardTotal` shards and returns the `shardNumber`th shard.
+ * Shards will differ in size by at most 1.
+ * Shard params must be 1 ≤ shardNumber ≤ shardTotal.
+ * @param {Array<Smokehouse.TestDfn>} testDefns
+ * @param {string=} shardArg
+ * @return {Array<Smokehouse.TestDfn>}
+ */
+function getShardedDefinitions(testDefns, shardArg) {
+  if (!shardArg) return testDefns;
+
+  // eslint-disable-next-line max-len
+  const errorMessage = `'shard' must be of the form 'n/d' and n and d must be positive integers with 1 ≤ n ≤ d. Got '${shardArg}'`;
+  const match = /^(?<shardNumber>\d+)\/(?<shardTotal>\d+)$/.exec(shardArg);
+  assert(match && match.groups, errorMessage);
+  const shardNumber = Number(match.groups.shardNumber);
+  const shardTotal = Number(match.groups.shardTotal);
+  assert(shardNumber > 0 && Number.isInteger(shardNumber), errorMessage);
+  assert(shardTotal > 0 && Number.isInteger(shardTotal));
+  assert(shardNumber <= shardTotal, errorMessage);
+
+  // Array is sharded with `Math.ceil(length / shardTotal)` shards first
+  // and then the remaining `Math.floor(length / shardTotal) shards.
+  // e.g. `[0, 1, 2, 3]` split into 3 shards is `[[0, 1], [2], [3]]`.
+  const baseSize = Math.floor(testDefns.length / shardTotal);
+  const biggerSize = baseSize + 1;
+  const biggerShardCount = testDefns.length % shardTotal;
+
+  // Since we don't have tests for this file, construct all shards so correct
+  // structure can be asserted.
+  const shards = [];
+  let index = 0;
+  for (let i = 0; i < shardTotal; i++) {
+    const shardSize = i < biggerShardCount ? biggerSize : baseSize;
+    shards.push(testDefns.slice(index, index + shardSize));
+    index += shardSize;
+  }
+  assert.equal(shards.length, shardTotal);
+  assert.deepEqual(shards.flat(), testDefns);
+
+  const shardDefns = shards[shardNumber - 1];
+  console.log(`In this shard (${shardArg}), running: ${shardDefns.map(d => d.id).join(' ')}\n`);
+  return shardDefns;
+}
+
 /**
  * Prune the `networkRequests` from the test expectations when `takeNetworkRequestUrls`
  * is not defined. Custom servers may not have this method available in-process.
@@ -163,6 +210,11 @@ async function begin() {
         default: false,
         describe: 'Run all available tests except the ones provided',
       },
+      'shard': {
+        type: 'string',
+        // eslint-disable-next-line max-len
+        describe: 'A argument of the form "n/d", which divides the selected tests into d groups and runs the nth group. n and d must be positive integers with 1 ≤ n ≤ d.',
+      },
     })
     .wrap(y.terminalWidth())
     .argv;
@@ -187,7 +239,8 @@ async function begin() {
   const {default: rawTestDefns} = await import(url.pathToFileURL(testDefnPath).href);
   const allTestDefns = updateTestDefnFormat(rawTestDefns);
   const invertMatch = argv.invertMatch;
-  const testDefns = getDefinitionsToRun(allTestDefns, requestedTestIds, {invertMatch});
+  const requestedTestDefns = getDefinitionsToRun(allTestDefns, requestedTestIds, {invertMatch});
+  const testDefns = getShardedDefinitions(requestedTestDefns, argv.shard);
 
   let smokehouseResult;
   let server;