test: add test-changed script

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)
+})