test: add test-changed script

package.json

@@ -5,7 +5,8 @@
     "packages/test/*"
   ],
   "scripts": {
-    "test": "jest --env node",
+    "test": "jest --env node --runInBand",
+    "test-changed": "node scripts/testChanged.js",
     "posttest": "yarn clean",
     "lint": "eslint --fix packages/**/*.js packages/**/bin/* test/**/*.js",
     "clean": "rimraf packages/test/*",
@@ -23,7 +24,8 @@
     "testPathIgnorePatterns": [
       "/template/",
       "/packages/test/",
-      "/temp/"
+      "/temp/",
+      ".*.helper.js"
     ]
   },
   "lint-staged": {

scripts/testChanged.js

@@ -0,0 +1,21 @@
+const execa = require('execa')
+
+const additionalArgs = process.argv.slice(2)
+
+;(async () => {
+  // get modified files
+  const { stdout } = await execa('git', ['ls-files', '--exclude-standard', '--modified', '--others'])
+  const files = stdout.split('\n').filter(line => /\.js$/.test(line))
+
+  await execa('jest', [
+    '--env', 'node',
+    '--runInBand',
+    ...additionalArgs,
+    '--findRelatedTests', ...files
+  ], {
+    stdio: 'inherit'
+  })
+})().catch(err => {
+  console.error(err)
+  process.exit(1)
+})