more unit tests and corresponding refactoring (#174)

package.json

@@ -4,14 +4,11 @@
   "description": "checkout action",
   "main": "lib/main.js",
   "scripts": {
-    "build": "tsc",
+    "build": "tsc && ncc build && node lib/misc/generate-docs.js",
     "format": "prettier --write **/*.ts",
     "format-check": "prettier --check **/*.ts",
     "lint": "eslint src/**/*.ts",
-    "pack": "ncc build",
-    "gendocs": "node lib/misc/generate-docs.js",
-    "test": "jest",
-    "all": "npm run build && npm run format && npm run lint && npm run pack && npm run gendocs && npm test"
+    "test": "jest"
   },
   "repository": {
     "type": "git",