add c8 test coverage (#533)

Author: romainmenke

lib/process-content.js

@@ -21,6 +21,7 @@ module.exports = function processContent(
   // SugarSS support:
   if (ext === ".sss") {
     if (!sugarss) {
+      /* c8 ignore next 3 */
       try {
         sugarss = require("sugarss")
       } catch {} // Ignore

package.json

@@ -27,6 +27,7 @@
   },
   "devDependencies": {
     "ava": "^5.0.0",
+    "c8": "^8.0.0",
     "eslint": "^8.2.0",
     "eslint-config-problems": "^7.0.0",
     "eslint-plugin-prettier": "^4.0.0",
@@ -42,7 +43,7 @@
     "ci": "eslint . && ava",
     "lint": "eslint . --fix",
     "pretest": "npm run lint",
-    "test": "ava"
+    "test": "c8 ava"
   },
   "eslintConfig": {
     "extends": "eslint-config-problems",