Firebase Stub: unit tests separated in different files

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

@@ -0,0 +1,51 @@
+import FirebaseStub, { AuthConstants } from '../../gatsby-plugin-firebase';
+
+test('reuses existing Auth instance', () => {
+  const auth1 = FirebaseStub.auth();
+  const auth2 = FirebaseStub.auth();
+
+  expect(auth1.uuid).toBeTruthy();
+  expect(auth2.uuid).toBeTruthy();
+  expect(auth1.uuid).toEqual(auth2.uuid);
+});
+
+test('returns anonymous user 1 when signing in anonymously', async () => {
+  const user = await FirebaseStub.auth().signInAnonymously();
+
+  expect(user).toBeTruthy();
+  expect(user).toEqual(AuthConstants.anonymousUser1);
+});
+
+test('calls onAuthStateChanged observer with anonymous user 1 when signing in anonymously', async () => {
+  let user = null;
+  let error = null;
+  FirebaseStub.auth().onAuthStateChanged(
+    (_user) => {
+      user = _user;
+    },
+    (_error) => {
+      error = _error;
+    },
+  );
+
+  await FirebaseStub.auth().signInAnonymously();
+
+  expect(user).toBeTruthy();
+  expect(user).toEqual(AuthConstants.anonymousUser1);
+  expect(error).toBeNull();
+});
+
+test('onAuthStateChanged unsubscribe removes observer', () => {
+  const observer = () => {};
+  const unsubscribe = FirebaseStub.auth().onAuthStateChanged(observer);
+  expect(unsubscribe).toBeTruthy();
+  expect(
+    FirebaseStub.auth().onAuthStateChangedObservers.indexOf(observer),
+  ).toBeGreaterThanOrEqual(0);
+
+  unsubscribe();
+
+  expect(
+    FirebaseStub.auth().onAuthStateChangedObservers.indexOf(observer),
+  ).not.toBeGreaterThanOrEqual(0);
+});