Fix RUTv2 tests by adding a fake functions directory. (#5363)

* Fix RUTv2 tests by adding a fake functions directory.

* Fix package.json.

* Commit yarn.lock.

Author: yuchenshi

packages/rules-unit-testing/firebase.json

@@ -1,6 +1,6 @@
 {
   "functions": {
-    "source": "."
+    "source": "./functions"
   },
   "storage": {
     "rules": "test/storage.rules"

packages/rules-unit-testing/functions/index.js

@@ -0,0 +1,3 @@
+// This is just a file to make the Functions emulator
+// start up correctly during tests. No function is declared.
+module.exports = {};

packages/rules-unit-testing/functions/package.json

@@ -0,0 +1,14 @@
+{
+  "name": "functions",
+  "version": "1.0.0",
+  "description": "Fake functions module for functions emulator.",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "private": true,
+  "dependencies": {
+    "firebase-admin": "9.11.1",
+    "firebase-functions": "3.15.4"
+  }
+}