test: add coverage (#58)

package.json

@@ -6,7 +6,9 @@
   "description": "GitHub Action for creating a GitHub App Installation Access Token",
   "scripts": {
     "build": "esbuild main.js post.js --bundle --outdir=dist --out-extension:.js=.cjs --platform=node --target=node16.16",
-    "test": "ava tests/index.js"
+    "test": "c8 --100 ava tests/index.js",
+    "coverage": "c8 report --reporter html",
+    "postcoverage": "open-cli coverage/index.html"
   },
   "license": "MIT",
   "dependencies": {
@@ -16,9 +18,11 @@
   },
   "devDependencies": {
     "ava": "^5.3.1",
+    "c8": "^8.0.1",
     "dotenv": "^16.3.1",
     "esbuild": "^0.19.4",
     "execa": "^8.0.1",
+    "open-cli": "^7.2.0",
     "undici": "^5.25.2"
   },
   "release": {