FirebaseStub: added more unit tests related to auth

__mocks__/__tests__/gatsby-plugin-firebase/auth.signInWithPopup.test.js

@@ -0,0 +1,54 @@
+import FirebaseStub, { AuthConstants } from '../../gatsby-plugin-firebase';
+
+describe('with Google auth provider', () => {
+  test('sets current user to Google user 3', async () => {
+    await FirebaseStub.auth().signInWithPopup(
+      new FirebaseStub.auth.GoogleAuthProvider(),
+    );
+
+    const { currentUser } = FirebaseStub.auth();
+    expect(currentUser).toBeTruthy();
+    expect(currentUser.uid).toEqual(AuthConstants.googleUser3.uid);
+  });
+
+  test('sets current user provider data', async () => {
+    const provider = new FirebaseStub.auth.GoogleAuthProvider();
+    await FirebaseStub.auth().signInWithPopup(provider);
+
+    const { currentUser } = FirebaseStub.auth();
+    expect(currentUser).toBeTruthy();
+    expect(currentUser.providerData).toBeTruthy();
+    expect(currentUser.providerData).toHaveLength(1);
+    expect(currentUser.providerData[0].providerId).toEqual(provider.providerId);
+  });
+
+  test('calls onAuthStateChanged observer with Google user 3', async () => {
+    let user = null;
+    let error = null;
+    FirebaseStub.auth().onAuthStateChanged(
+      (_user) => {
+        user = _user;
+      },
+      (_error) => {
+        error = _error;
+      },
+    );
+
+    await FirebaseStub.auth().signInWithPopup(
+      new FirebaseStub.auth.GoogleAuthProvider(),
+    );
+
+    expect(user).toBeTruthy();
+    expect(user.uid).toEqual(AuthConstants.googleUser3.uid);
+    expect(error).toBeNull();
+  });
+
+  test('returns Google user 3', async () => {
+    const user = await FirebaseStub.auth().signInWithPopup(
+      new FirebaseStub.auth.GoogleAuthProvider(),
+    );
+
+    expect(user).toBeTruthy();
+    expect(user.uid).toEqual(AuthConstants.googleUser3.uid);
+  });
+});