Update mockConfig function for v4 firebase-functions (#173)

V4 Functions SDK does not expose the config singleton directly.

Use the internal-only `resetCache` function instead.

Author: taeold

spec/main.spec.ts

@@ -340,11 +340,5 @@ describe('main', () => {
 
       expect(functions.config()).to.deep.equal(config);
     });
-
-    it('should not throw an error when functions.config.singleton is missing', () => {
-      delete functions.config.singleton;
-
-      expect(() => mockConfig(config)).to.not.throw(Error);
-    });
   });
 });

src/v1.ts

@@ -32,6 +32,8 @@ import {
   firestore,
   HttpsFunction,
   Runnable,
+  // @ts-ignore
+  resetCache,
 } from 'firebase-functions';
 
 /** Fields of the event context that can be overridden/customized. */
@@ -345,9 +347,8 @@ export function makeChange<T>(before: T, after: T): Change<T> {
 
 /** Mock values returned by `functions.config()`. */
 export function mockConfig(conf: { [key: string]: { [key: string]: any } }) {
-  if (config.singleton) {
-    delete config.singleton;
+  if (resetCache) {
+    resetCache();
   }
-
   process.env.CLOUD_RUNTIME_CONFIG = JSON.stringify(conf);
 }