fix: serialize test files (#121)

Author: seriousme

package.json

@@ -9,7 +9,7 @@
   "scripts": {
     "lint": "eslint",
     "lint:fix": "eslint --fix",
-    "unit": "node --test --test-timeout=180000 test/*.js",
+    "unit": "node --test --test-timeout=180000 --test-concurrency=1 test/*.js",
     "test": "npm run lint && npm run unit",
     "coverage": "c8 --reporter=lcov npm run unit",
     "license-checker": "license-checker --production --onlyAllow='MIT;ISC;BSD-3-Clause;BSD-2-Clause;Apache-2.0;Apache*'",