Delete Account unit tests: added tests related to Google reauthentication

__mocks__/gatsby-plugin-firebase/auth/authProvider.js

@@ -0,0 +1,23 @@
+/* eslint-disable no-underscore-dangle */
+class AuthProvider {
+  /**
+   * Creates a new auth provider.
+   *
+   * @param {string} providerId Provider ID.
+   */
+  constructor(providerId) {
+    if (!providerId) {
+      throw new Error('providerId must be provided.');
+    } else if (typeof providerId !== 'string') {
+      throw new Error('providerId should be a string.');
+    } else {
+      this._providerId = providerId;
+    }
+  }
+
+  get providerId() {
+    return this._providerId;
+  }
+}
+
+export default AuthProvider;