Lazy loading the Firestore implementation (#110)

* Lazy loading the Firestore implementation

* Integration tests for module lazy loading

* Extracted variable in test

Author: hiranya911

src/firestore/firestore.ts

@@ -111,5 +111,8 @@ function initFirestore(app: FirebaseApp): Firestore {
         'to use Cloud Firestore API.',
     });
   }
-  return new Firestore(options);
+
+  // Lazy-load the Firestore implementation here, which in turns loads gRPC.
+  let firestoreDatabase = require('@google-cloud/firestore');
+  return new firestoreDatabase(options);
 }

test/integration/index.js

@@ -97,6 +97,34 @@ utils.assert(
   'admin.messaging(app).app',
   'App instances do not match.'
 );
+utils.assert(
+  _.isEqual(admin.storage(nonNullApp).app, nonNullApp),
+  'admin.storage(app).app',
+  'App instances do not match.'
+);
+
+// Firestore should not be loaded yet.
+var gcloud = require.cache[require.resolve('@google-cloud/firestore')];
+utils.assert(
+  typeof gcloud === 'undefined',
+  'require(firebase-admin)',
+  'Firestore module already loaded'
+);
+
+// Calling admin.firestore should load Firestore
+const firestoreNamespace = admin.firestore;
+utils.assert(
+  typeof firestoreNamespace !== 'undefined',
+  'admin.firestore',
+  'Firestore namespace could not be loaded.'
+);
+
+gcloud = require.cache[require.resolve('@google-cloud/firestore')];
+utils.assert(
+  typeof gcloud !== 'undefined',
+  'admin.firestore',
+  'Firestore module not loaded'
+);
 
 /**
  * Prompts the developer whether the Database rules should be