Update test linting

.eslintrc

@@ -2,6 +2,11 @@
   "extends": "eslint:recommended",
   "env": {
     "node": true,
+    "es6": true,
+    "jest": true
+  },
+  "globals": {
+    "testRule": "readonly"
   },
   "rules": {
     "comma-dangle": [2, "always-multiline"],
@@ -24,5 +29,6 @@
     "space-before-blocks": [2, "always"],
     "space-in-parens": [2, "never"],
     "space-unary-ops": 2,
-  }
+  },
+  "plugins": ["jest"]
 }