Add a type checking command and declare test packages

declarations.d.ts

@@ -0,0 +1,12 @@
+// These packages are not actually used but are used in the test input/output
+// to verify the transform functionality. They're declared here so type-checking
+// can still be performed on all files.
+declare module "react";
+declare module "@fortawesome/free-brands-svg-icons";
+declare module "@fortawesome/free-solid-svg-icons";
+declare module "@fortawesome/free-regular-svg-icons";
+declare module "@fortawesome/pro-regular-svg-icons";
+declare module "@fortawesome/pro-solid-svg-icons";
+declare module "@fortawesome/pro-light-svg-icons";
+declare module "@fortawesome/react-fontawesome";
+declare module "custom-design-system";

package.json

@@ -6,7 +6,8 @@
   "author": "Spencer Miskoviak <smiskoviak@gmail.com>",
   "license": "MIT",
   "scripts": {
-    "test": "jest"
+    "test": "jest",
+    "check:types": "tsc --noEmit"
   },
   "devDependencies": {
     "@types/jest": "^24.0.18",