Prototype Locally With Flutter and Firebase

Never mess up your online database again

Jackson Zhou
Jan 14 · 4 min read
Photo by “My Life Through A Lens” on Unsplash

Flutter is a cross-platform app front-end framework and Firebase is an app back-end platform. They are often used together.

As Flutter and Firebase use different languages (Dart and Node.js), testing/prototyping both together in a contained local environment is a non-trivial problem.

Note: Online testing is not preferable because it corrupts the database and requires a complicated setup (deploy and version matching).

We can achieve local testing with the Firebase Emulator Suite which is a mocked Firebase service.

The following diagram shows how Flutter apps interact with the Firebase Emulator Suite:

credit: Firebase documentation

Let’s go through how to use Flutter with the Firebase Emulator suite step-by-step.

Note: The code used to illustrate in this post comes from my side-project. Although we mainly focus on Flutter with Firebase, with a few changes, it will apply to X + Firebase where X can be React Native, Cordova, etc.

Step 1: Install Firebase Emulator Suite

Firebase Emulator Suite comes with the Firebase CLI which can be installed with the following command:

npm install -g firebase-tools

Step 2: Bypass Authentication Step in Emulation

As shown in the diagram above, Firebase authentication is not part of the Firebase Emulator Suite. Consequently, data authentication/authorization won’t work locally, so they have to be mocked.

There are many ways to mock authentication. I used the environment variable set by the Firebase Emulator Suite to mock:

Example mocked authentication implementation from tianhaoz95/iwfp

Step 3: Connect the Flutter App to Firebase Emulator Suite

We want to connect Firebase Cloud function callables to localhost:

Example to connect Firebase Cloud Function callables to Firebase Emulator Suite from tianhaoz95/iwfp

Note: We want to use a top-level environment to control the local vs. cloud. There are many ways to achieve this. For example, setting an environment variable or using different entry points.

Here is an example of using different entry points:

Step 4: Enable HTTP (No “S”) Connection (iOS Only)

iOS doesn’t allow any HTTP requests by default.

To allow HTTP connections to localhost only, add the following snippet into [flutter_project_root]/ios/Runner/info.plist:

iOS configuration from tianhaoz95/iwfp inspired by this GitHub issue

Step 5: Start Tests Locally

Running the following command in your Firebase project directory will start the tests:

npm run build &&
firebase emulators:exec --only functions,firestore \"cd ../../flutter_app && flutter drive --target=test_driver/emulator.dart\""


  • firebase emulator:exec takes a second argument as the command to execute on top of starting the emulator. In our case, that is cd ../../flutter_app && flutter drive --target=test_driver/emulator.dart, meaning we want to first navigate to Flutter and start our integration tests.
  • npm run build is important here because the emulator takes transpiled code only.
  • It’s also a good idea to add the script into your package.json as npm run hermetic-device-test so that you won’t have to remember such a long command.
  • Alternatively, you can run the Emulator and Flutter apps separately for interactive debugging/development with firebase emulators:exec --only functions,firestore in one terminal and flutter run in another.

Step 6: Have a Cup of Coffee

The tests will look like this (refer to image caption for each execution stage):

Firebase Emulator Suite bootup from tianhaoz95/iwfp
Firebase Emulator Suite API deployment from tianhaoz95/iwfp
Flutter integration test result running within Firebase Emulator Suite from tianhaoz95/iwfp

Now you never have to worry about apps in development messing up the database again. Happy hacking with Flutter and Firebase.

Better Programming

Advice for programmers.

Jackson Zhou

Written by

Hold my boba, cuz I need to write code. I explore new tech every day (currently Flutter). Subscribe to my latest content at

Better Programming

Advice for programmers.

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