Add basic unit tests

package.json

@@ -5,7 +5,8 @@
   "private": true,
   "scripts": {
     "build": "ncc build src/setup-elixir.js",
-    "format": "prettier \"src/**/*.js\""
+    "format": "prettier \"src/**/*.js\"",
+    "test": "jest"
   },
   "husky": {
     "hooks": {
@@ -16,11 +17,12 @@
     "@actions/core": "^1.0.0",
     "@actions/exec": "^1.0.0",
     "@actions/tool-cache": "^1.1.0",
-    "semver": "^6.3.0"
+    "semver": "^7.3.2"
   },
   "devDependencies": {
     "@zeit/ncc": "^0.22.1",
     "husky": "^4.2.5",
+    "jest": "^26.4.2",
     "prettier": "^2.0.5"
   }
 }