Testing with watermelon db

I've been working on an open-source cycling computer with my brother for a few weeks now. It's built with react-native expo and because it's a fairly data intensive and reactive we naturally landed on watermelon db for our database/ORM.

Their docs are great but are a little light on how to test your watermelon backed app.

The setup

When you run your react-native app with jest it'll run in a react-native like environment with many of the mobile API'S mocked out because the test suite isn't running on a real device. If you try run jest test with watermelon you'll likely run into this error:

Diagnostic error: NativeModules.DatabaseBridge is not defined! This means that you haven\'t properly linked WatermelonDB native module. Refer to docs for more details

This is telling us that the native API isn't implemented. To get our tests running we need to mock this interaction. I found this suggestion to use lokijs adapter which uses an in memory db instead of the sqlite lib, this worked great but it doesn't support raw queries. We use raw SQL queries in a few cases that are too complex for the ORM, so we needed another solution.

Watermelon also works in a node.js environment which loads real sqlite bindings. To do this you need to intercept the imports in jest and load the node.js adapter.

First install the node.js sqlite dependencies:

yarn add --dev better-sqlite3

Then intercept the native calls and load the node module.

// setup.js

  () => {
    return jest.requireActual(

Now our sqlite dispatcher will issue sqlite queries via better-sqlite3 rather than the native bridge.


Next we'll also want to clear our database between each test. So I added the following jest hook after each test.

afterEach(async () => {
  await db.write(async () => {
    await db.unsafeResetDatabase();

Now you are ready to run a test, remember to run any calls to the database in a render.act(). For example:

it('Widget page renders & updates correctly', async () => {
  // write the first realtime row.
  const powerProps = {
    title: 'Power ',
    icon: 'lightning-bolt',

  let record = await getOrCreateRealtimeRecord();
  let updatedRecord!: RealtimeDataModel;

  // Check the widget is using the realtime table.
  // initial value should be 0
  const widget = screen.findByProps({...powerProps, data: null});

  // write to the db updating the realtime table.
  await renderer.act(async () => {
    updatedRecord = await updateRealTimeRecord(record);

  // again check the component to see that it's re-rendered correctly
  const updatedWidget = tree.root.findByProps({
    data: updatedRecord.instantPower,

That should be it! Let me know if you have any issues.