Tweak test configs for better memory use

Author: jdalton

.env.test

@@ -1,2 +1,3 @@
 NODE_COMPILE_CACHE="./.cache"
+NODE_OPTIONS="--max-old-space-size=4096 --max-semi-space-size=512"
 VITEST=1

vitest.config.mts

@@ -2,6 +2,27 @@ import { defineConfig } from 'vitest/config'
 
 export default defineConfig({
   test: {
+    globals: false,
+    environment: 'node',
+    include: ['test/**/*.test.{js,ts,mjs,cjs}'],
+    reporters: ['default'],
+    // Improve memory usage by running tests sequentially in CI.
+    pool: 'forks',
+    poolOptions: {
+      forks: {
+        singleFork: true,
+        maxForks: 1,
+        // Isolate tests to prevent memory leaks between test files.
+        isolate: true,
+      },
+      threads: {
+        singleThread: true,
+        // Limit thread concurrency to prevent RegExp compiler exhaustion.
+        maxThreads: 1,
+      },
+    },
+    testTimeout: 60_000,
+    hookTimeout: 60_000,
     coverage: {
       provider: 'v8',
       reporter: ['text', 'json', 'html'],