Executing test files in parallel, for ~5x better performance

Author: fabiospampinato

package-lock.json

@@ -28,7 +28,7 @@
     "compile:watch": "tsc --outDir dist --watch",
     "format": "npm run compile && node dist/bin.js --write src test",
     "prepublishOnly": "npm run compile && npm run test",
-    "test": "cross-env NODE_OPTIONS=--experimental-vm-modules jest --runInBand --rootDir test/__tests__",
+    "test": "cross-env NODE_OPTIONS=--experimental-vm-modules jest --rootDir test/__tests__ --testTimeout 60000",
     "typecheck": "tsc --noEmit"
   },
   "peerDependencies": {
@@ -72,6 +72,7 @@
     "prettier": "3.3.3",
     "radix64-encoding": "^2.0.1",
     "tiny-dirname": "^1.0.1",
-    "typescript": "^5.4.5"
+    "typescript": "^5.4.5",
+    "zeptoid": "^1.0.2"
   }
 }

package.json

@@ -2,10 +2,11 @@ import once from "function-once";
 import * as Archive from "json-archive";
 import exec from "nanoexec";
 import fs from "node:fs/promises";
+import os from "node:os";
 import path from "node:path";
 import process from "node:process";
-import { setTimeout as delay } from "node:timers/promises";
 import Base64 from "radix64-encoding";
+import zeptoid from "zeptoid";
 
 import { expect, test } from "@jest/globals";
 import serializerRaw from "jest-snapshot-serializer-raw";
@@ -17,12 +18,12 @@ expect.addSnapshotSerializer(serializerAnsi);
 const ROOT_PATH = process.cwd();
 const BIN_PATH = path.join(ROOT_PATH, "dist", "bin.js");
 const FIXTURES_PATH = path.join(ROOT_PATH, "test", "__fixtures__");
+const TESTS_PATH = path.join(ROOT_PATH, "test");
 
 async function getArchive(folderPath) {
   const packPrev = await Archive.pack(folderPath);
   const archive = {
-    getPack: once(async () => {
-      await delay(100); // Giving a little time for the FS to settle
+    getPack: once(() => {
       return Archive.pack(folderPath);
     }),
     getChanged: once(async () => {
@@ -65,6 +66,27 @@ function getFixturesPath(dir) {
   return path.join(FIXTURES_PATH, dir);
 }
 
+async function getIsolatedFixtures(dir) {
+  const [rootPart, ...subParts] = dir.split("/");
+  const fixturesPath = getFixturesPath(rootPart);
+  const tempPath = await getTempPath(`prettier-${rootPart}`);
+  const tempGitPath = path.join(tempPath, ".git");
+  const isolatedPath = path.join(tempPath, ...subParts);
+
+  await fs.mkdir(tempPath, { recursive: true });
+  await fs.mkdir(tempGitPath, { recursive: true });
+  await fs.cp(fixturesPath, tempPath, { recursive: true });
+
+  const dispose = () => {
+    return fs.rm(tempPath, { recursive: true, force: true });
+  };
+
+  return {
+    path: isolatedPath,
+    dispose,
+  };
+}
+
 function getNormalizedOutput(output, options) {
   // \r is trimmed from jest snapshots by default;
   // manually replacing this character with /*CR*/ to test its true presence
@@ -74,9 +96,16 @@ function getNormalizedOutput(output, options) {
   return output;
 }
 
+async function getTempPath(prefix) {
+  const rootPath = await fs.realpath(os.tmpdir());
+  const tempPath = path.join(rootPath, `${prefix}-${zeptoid()}`);
+  return tempPath;
+}
+
 async function runCommand(dir, args, options) {
-  const cwd = getFixturesPath(dir);
-  const archive = dir ? await getArchive(cwd) : undefined;
+  const fixtures = dir ? await getIsolatedFixtures(dir) : undefined;
+  const archive = fixtures ? await getArchive(fixtures.path) : undefined;
+  const cwd = fixtures ? fixtures.path : TESTS_PATH;
   const argsWithReplacements = args.map((arg) => arg.replaceAll("$CWD", cwd));
   const result = exec("node", [BIN_PATH, ...argsWithReplacements], { cwd, stdio: "pipe" });
 
@@ -90,7 +119,7 @@ async function runCommand(dir, args, options) {
   const stderr = getNormalizedOutput((await result.stderr).toString());
   const write = (await archive?.getDiff()) || [];
 
-  await archive?.reset();
+  await fixtures?.dispose();
 
   return { status, stdout, stderr, write };
 }