Added module for test-utilities used across all packages

Summary: Added new package with test utilities re-used by other packages

Reviewed By: mweststrate

Differential Revision: D21949629

fbshipit-source-id: 8bfa959401669dc8911a1f647f417cafd92c2e4b

desktop/plugin-lib/tsconfig.json

@@ -4,6 +4,7 @@
     "outDir": "lib",
     "rootDir": "src"
   },
+  "references": [{"path": "../test-utils"}],
   "include": ["src"],
   "exclude": ["node_modules", "**/__tests__/*"]
 }