add testing GKs

Summary: Adding two GKs (one failing, one passing) to allow the testing of gatekeeper functionality. This is used in the next diff.

Reviewed By: jknoxville

Differential Revision: D13082651

fbshipit-source-id: c6d8ef484564c8ae8b4c107de5643c700f696ad5

src/fb-stubs/GK.js

@@ -7,10 +7,16 @@
 
 export type GKID = string;
 
+export const TEST_PASSING_GK = 'TEST_PASSING_GK';
+export const TEST_FAILING_GK = 'TEST_FAILING_GK';
+
 export default class GK {
   static init() {}
 
   static get(id: GKID): boolean {
+    if (process.env.NODE_ENV === 'test' && id === TEST_PASSING_GK) {
+      return true;
+    }
     return false;
   }
 }