Mocking Native Modules

Q: Does jest-expo mock every Expo module?

It mocks the majority of expo-* packages shipped with the SDK. Custom native modules, bare third-party SDKs, and some community packages are not covered - add jest.mock manually.

Q: Where do I put shared mocks?

App-wide: jest.setup.ts (fonts, splash screen, constants). Feature-specific: top of the test file or __tests__/helpers/. Package-style: __mocks__/expo-location.ts at project root for jest.mock("expo-location") auto-resolution.

Q: jest.mock vs jest.spyOn?

jest.mock replaces the entire module - use for native bridges. jest.spyOn wraps one method - use when most of the module should stay real (rare with native modules in Jest).

Q: How do I mock expo-router?

Prefer renderRouter from expo-router/testing-library over mocking useRouter when testing navigation. For leaf components, pass navigation callbacks as props instead of mocking the router hook.

Q: Can I mock only one function in a module?

Use sparingly - requireActual on native-heavy modules can fail; a thin wrapper module is safer.

Q: Why does my mock not apply?

jest.mock must be at module scope (hoisted), not inside it/beforeEach. Ensure the import path matches exactly what production code imports. Clear Metro/Jest cache: npx jest --clearCache.

Q: Should I mock fetch or the API client?

Mock src/api/client or the TanStack Query queryFn wrapper - not both. One boundary keeps tests focused on how the app handles success and error responses.

Jest runs in Node - there is no camera, GPS, or Keychain. jest-expo stubs most Expo SDK modules with safe defaults; you add manual mocks when your tests need specific permission results, sensor readings, or third-party native SDK behavior.

Recipe

Quick-reference recipe card - copy-paste ready.

// __tests__/location-screen-test.tsx
import { render, screen, waitFor } from "@testing-library/react-native";
import * as Location from "expo-location";
import { LocationScreen } from "../src/screens/location-screen";
 
jest.mock("expo-location");
 
const mockLocation = jest.mocked(Location);
 
beforeEach(() => {
  mockLocation.requestForegroundPermissionsAsync.mockResolvedValue({
    status: "granted",
    granted: true,
    canAskAgain: true,
    expires: "never",
  });
 
  mockLocation.getCurrentPositionAsync.mockResolvedValue({
    coords: { latitude: 37.77, longitude: -122.42, altitude: 0, accuracy: 5, altitudeAccuracy: 5, heading: 0, speed: 0 },
    timestamp: 1_700_000_000_000,
  });
});
 
test("shows coordinates when permission is granted", async () => {
  render(<LocationScreen />);
  expect(await screen.findByText(/37\.77/)).toBeOnTheScreen();
  await waitFor(() => {
    expect(mockLocation.getCurrentPositionAsync).toHaveBeenCalled();
  });
});

When to reach for this:

Components call expo-location, expo-notifications, expo-secure-store, or other native bridges.
Custom Expo modules or React Native native modules your app imports directly.
Simulating permission denial, offline storage failures, or SDK error codes.
Spying on module calls to assert your app reacts correctly - not to skip writing assertions.

Working Example

// src/services/push-token-service.ts
import * as Notifications from "expo-notifications";
import * as Device from "expo-device";
 
export async function registerForPushNotifications(): Promise<string | null> {
  if (!Device.isDevice) {
    return null;
  }
 
  const { status: existing } = await Notifications.getPermissionsAsync();
  let finalStatus = existing;
 
  if (existing !== "granted") {
    const { status } = await Notifications.requestPermissionsAsync();
    finalStatus = status;
  }
 
  if (finalStatus !== "granted") {
    throw new Error("Push permission denied");
  }
 
  const token = await Notifications.getExpoPushTokenAsync();
  return token.data;
}

// __tests__/push-token-service-test.tsx
import * as Notifications from "expo-notifications";
import * as Device from "expo-device";
import { registerForPushNotifications } from "../src/services/push-token-service";
 
jest.mock("expo-notifications");
jest.mock("expo-device");
 
const notifications = jest.mocked(Notifications);
const device = jest.mocked(Device);
 
describe("registerForPushNotifications", () => {
  beforeEach(() => {
    jest.clearAllMocks();
    device.isDevice = true;
  });
 
  test("returns token when permission already granted", async () => {
    notifications.getPermissionsAsync.mockResolvedValue({
      status: "granted",
      granted: true,
      canAskAgain: true,
      expires: "never",
    });
    notifications.getExpoPushTokenAsync.mockResolvedValue({
      data: "ExponentPushToken[abc]",
      type: "expo",
    });
 
    await expect(registerForPushNotifications()).resolves.toBe(
      "ExponentPushToken[abc]"
    );
    expect(notifications.requestPermissionsAsync).not.toHaveBeenCalled();
  });
 
  test("requests permission when not yet granted", async () => {
    notifications.getPermissionsAsync.mockResolvedValue({
      status: "undetermined",
      granted: false,
      canAskAgain: true,
      expires: "never",
    });
    notifications.requestPermissionsAsync.mockResolvedValue({
      status: "granted",
      granted: true,
      canAskAgain: true,
      expires: "never",
    });
    notifications.getExpoPushTokenAsync.mockResolvedValue({
      data: "ExponentPushToken[xyz]",
      type: "expo",
    });
 
    await expect(registerForPushNotifications()).resolves.toBe(
      "ExponentPushToken[xyz]"
    );
    expect(notifications.requestPermissionsAsync).toHaveBeenCalledTimes(1);
  });
 
  test("throws when permission denied", async () => {
    notifications.getPermissionsAsync.mockResolvedValue({
      status: "denied",
      granted: false,
      canAskAgain: false,
      expires: "never",
    });
 
    await expect(registerForPushNotifications()).rejects.toThrow(
      "Push permission denied"
    );
  });
 
  test("returns null on simulator", async () => {
    device.isDevice = false;
 
    await expect(registerForPushNotifications()).resolves.toBeNull();
    expect(notifications.getPermissionsAsync).not.toHaveBeenCalled();
  });
});

What this demonstrates:

jest.mock("expo-*") - replaces the module with auto-mocked functions you configure per test.
jest.mocked() - typed access to mock implementations in TypeScript.
Service-layer tests - native calls isolated in one module; UI tests mock the service instead of three Expo packages.
Explicit permission branches - each status (granted, denied, undetermined) gets its own test.
jest.clearAllMocks() in beforeEach - prevents call-count leakage between tests.

Deep Dive

How It Works

jest-expo preset installs default mocks for Expo modules so imports do not crash Jest. Defaults return resolved promises with generic "success" shapes - rarely matching your production edge cases.
jest.mock("module-name") hoists to the top of the file and swaps the module before your imports evaluate. Works for expo-*, @react-native-async-storage/async-storage, and app-local modules.
Manual mocks in __mocks__/ next to node_modules package name or src/ file apply when you call jest.mock without a factory.
Spy pattern - jest.spyOn(module, "fn") wraps a single function while leaving the rest real (when not fully mocked).
Boundary mocking - mock src/services/api.ts, not fetch and not every transitive import, unless testing the HTTP client itself.

What jest-expo Mocks vs What You Must Mock

Category	jest-expo default	You override when
`expo-constants`, `expo-font`	Safe stubs	App reads specific `extra` config values
`expo-location`, `expo-camera`	Generic granted/success	Testing denial, timeout, or sensor errors
`expo-notifications`	Basic async fns	Permission flows and token shapes
Custom native module	Not mocked	Always - provide manual mock or wrapper
Third-party RN SDK (analytics, ads)	Not mocked	Mock at import site or facade module

Manual Mock Patterns

Inline factory (per test file):

jest.mock("expo-secure-store", () => ({
  getItemAsync: jest.fn(),
  setItemAsync: jest.fn(),
  deleteItemAsync: jest.fn(),
}));

Shared manual mock file:

src/
  services/
    analytics.ts
  __mocks__/
    analytics.ts      # manual mock - jest.mock("../services/analytics") picks it up

// src/__mocks__/analytics.ts
export const trackEvent = jest.fn();
export const identifyUser = jest.fn();

Re-export real module with one spy:

jest.mock("expo-linking", () => {
  const actual = jest.requireActual<typeof import("expo-linking")>("expo-linking");
  return {
    ...actual,
    openURL: jest.fn(actual.openURL),
  };
});

Avoiding False Confidence

Passing Jest test	Still verify on device
Mocked camera returns a URI	Real camera permissions and capture pipeline
Mocked biometrics always succeeds	Face ID / fingerprint failure UI
Mocked push token string	APNs/FCM registration on physical hardware
Mocked deep link URL	OS opening the app from cold start

Treat Jest native mocks as contract tests for your JS reaction - not proof the native bridge works. Add Maestro E2E or manual QA for permission dialogs and hardware paths.

TypeScript Notes

import type { LocationObject } from "expo-location";
 
function buildLocation(overrides: Partial<LocationObject> = {}): LocationObject {
  return {
    coords: {
      latitude: 0,
      longitude: 0,
      altitude: 0,
      accuracy: 0,
      altitudeAccuracy: 0,
      heading: 0,
      speed: 0,
    },
    timestamp: Date.now(),
    ...overrides,
  };
}
 
mockLocation.getCurrentPositionAsync.mockResolvedValue(
  buildLocation({ coords: { latitude: 51.5, longitude: -0.12, altitude: 0, accuracy: 1, altitudeAccuracy: 1, heading: 0, speed: 0 } })
);

Import types from the real package even when the implementation is mocked.
Use jest.mocked(fn) instead of (fn as jest.Mock) for stricter typing.
Factory mocks can call jest.requireActual to preserve unmocked exports and reduce drift.

Gotchas

Assuming jest-expo defaults match your test - Default permission mocks often return granted. Tests never exercise denial paths unless you override. Fix: Set mockResolvedValue for each permission/status scenario explicitly.
Mocking too deep - Mocking react-native internals or every expo-* import makes tests brittle when SDK updates changes signatures. Fix: Mock your service boundary; keep one module responsible for native calls.
Forgetting jest.clearAllMocks() - Call counts and queued implementations leak across tests. Fix: afterEach in jest.setup.ts or beforeEach in describe blocks that use spies.
jest.requireActual after full mock - Spreading requireActual for native modules can pull real native bindings into Jest and crash. Fix: Mock only the functions you call; avoid requireActual on modules that touch native code.
False confidence from green suites - All native behavior faked; production still fails on a real device. Fix: Document which flows need Maestro or manual device checks in PR templates.
Dynamic import() bypassing mocks - Lazy imports may resolve before jest.mock applies if mis-ordered. Fix: Use static imports in code under test, or jest.unstable_mockModule for ESM dynamic import paths.
Duplicating mock setup in every file - Copy-pasted expo-font mocks drift. Fix: Shared helpers in test-utils/native-mocks.ts or global mocks in jest.setup.ts for app-wide modules (fonts, splash screen).

Alternatives

Alternative	Use When	Don't Use When
`jest-expo` auto-mocks	Default - module imports should not crash Jest	You need realistic permission denial without overrides
Inline `jest.mock` factory	Per-test-file control of return values	Same mock repeated in 20 files - extract a helper
`__mocks__/` manual files	Shared mock across many tests	One-off behavior only used once
Service facade + mock facade	Clean architecture, swappable implementations	Throwaway prototype with no service layer
Maestro / Detox on device	Real OS permissions and native UI	Fast feedback on pure logic branches
`@shopify/react-native-skia` mock community packages	Heavy native deps with published Jest shims	Expo modules already covered by `jest-expo`

FAQs

Does jest-expo mock every Expo module?

It mocks the majority of expo-* packages shipped with the SDK. Custom native modules, bare third-party SDKs, and some community packages are not covered - add jest.mock manually.

Where do I put shared mocks?

App-wide: jest.setup.ts (fonts, splash screen, constants).
Feature-specific: top of the test file or __tests__/helpers/.
Package-style: __mocks__/expo-location.ts at project root for jest.mock("expo-location") auto-resolution.

jest.mock vs jest.spyOn?

jest.mock replaces the entire module - use for native bridges.
jest.spyOn wraps one method - use when most of the module should stay real (rare with native modules in Jest).

How do I mock AsyncStorage?

jest.mock("@react-native-async-storage/async-storage", () =>
  require("@react-native-async-storage/async-storage/jest/async-storage-mock")
);

The package ships an official Jest mock - prefer it over hand-rolled key-value objects.

How do I mock expo-router?

Prefer renderRouter from expo-router/testing-library over mocking useRouter when testing navigation. For leaf components, pass navigation callbacks as props instead of mocking the router hook.

Can I mock only one function in a module?

jest.mock("expo-linking", () => ({
  ...jest.requireActual("expo-linking"),
  openURL: jest.fn(() => Promise.resolve(true)),
}));

Use sparingly - requireActual on native-heavy modules can fail; a thin wrapper module is safer.

Why does my mock not apply?

jest.mock must be at module scope (hoisted), not inside it/beforeEach.
Ensure the import path matches exactly what production code imports.
Clear Metro/Jest cache: npx jest --clearCache.

Should I mock fetch or the API client?

Mock src/api/client or the TanStack Query queryFn wrapper - not both. One boundary keeps tests focused on how the app handles success and error responses.

How do I simulate permission denial?

mockLocation.requestForegroundPermissionsAsync.mockResolvedValue({
  status: "denied",
  granted: false,
  canAskAgain: false,
  expires: "never",
});

Match the shape from the real Expo module's TypeScript types - incomplete objects cause false positives.

What is false confidence?

Tests pass because mocks always return success, while real users hit denial dialogs, airplane mode, or OS bugs. Complement Jest with Maestro E2E for permission and OS-integration paths.

How do I test a custom Expo native module?

Create a TypeScript facade that imports your module. In Jest, jest.mock("@/modules/my-native-module") with a manual mock returning the JS API your app expects. Validate the real module on device builds.

Do mocks belong in setupFilesAfterEnv?

Only for modules every test needs (fonts, splash, reanimated silence). Feature mocks belong next to the tests that assert on them - global mocks hide missing setup in new tests.

How do I reset mocks between tests?

afterEach(() => {
  jest.clearAllMocks(); // clears call history
  // jest.resetAllMocks(); // also resets implementations - use when tests override mockResolvedValue
});

Add to jest.setup.ts for project-wide consistency.

Jest Setup for Expo - jest-expo preset and global setup
React Native Testing Library - assert UI after mocks resolve
Mobile Testing Basics - what belongs in unit vs E2E layers
Maestro E2E - real device flows mocks cannot replace
Expo Modules Core - how native modules expose JS APIs
Native Modules Basics - custom bridges that always need manual mocks

Stack versions: This page was written for React 19.2.3, React Native 0.86.0, and Expo SDK 57 (expo ~57.0.4).

Recipe

Quick-reference recipe card - copy-paste ready.

// __tests__/location-screen-test.tsx
import { render, screen, waitFor } from "@testing-library/react-native";
import * as Location from "expo-location";
import { LocationScreen } from "../src/screens/location-screen";
 
jest.mock("expo-location");
 
const mockLocation = jest.mocked(Location);
 
beforeEach(() => {
  mockLocation.requestForegroundPermissionsAsync.mockResolvedValue({
    status: "granted",
    granted: true,
    canAskAgain: true,
    expires: "never",
  });
 
  mockLocation.getCurrentPositionAsync.mockResolvedValue({
    coords: { latitude: 37.77, longitude: -122.42, altitude: 0, accuracy: 5, altitudeAccuracy: 5, heading: 0, speed: 0 },
    timestamp: 1_700_000_000_000,
  });
});
 
test("shows coordinates when permission is granted", async () => {
  render(<LocationScreen />);
  expect(await screen.findByText(/37\.77/)).toBeOnTheScreen();
  await waitFor(() => {
    expect(mockLocation.getCurrentPositionAsync).toHaveBeenCalled();
  });
});

When to reach for this:

Components call expo-location, expo-notifications, expo-secure-store, or other native bridges.
Custom Expo modules or React Native native modules your app imports directly.
Simulating permission denial, offline storage failures, or SDK error codes.
Spying on module calls to assert your app reacts correctly - not to skip writing assertions.

Working Example

// src/services/push-token-service.ts
import * as Notifications from "expo-notifications";
import * as Device from "expo-device";
 
export async function registerForPushNotifications(): Promise<string | null> {
  if (!Device.isDevice) {
    return null;
  }
 
  const { status: existing } = await Notifications.getPermissionsAsync();
  let finalStatus = existing;
 
  if (existing !== "granted") {
    const { status } = await Notifications.requestPermissionsAsync();
    finalStatus = status;
  }
 
  if (finalStatus !== "granted") {
    throw new Error("Push permission denied");
  }
 
  const token = await Notifications.getExpoPushTokenAsync();
  return token.data;
}

// __tests__/push-token-service-test.tsx
import * as Notifications from "expo-notifications";
import * as Device from "expo-device";
import { registerForPushNotifications } from "../src/services/push-token-service";
 
jest.mock("expo-notifications");
jest.mock("expo-device");
 
const notifications = jest.mocked(Notifications);
const device = jest.mocked(Device);
 
describe("registerForPushNotifications", () => {
  beforeEach(() => {
    jest.clearAllMocks();
    device.isDevice = true;
  });
 
  test("returns token when permission already granted", async () => {
    notifications.getPermissionsAsync.mockResolvedValue({
      status: "granted",
      granted: true,
      canAskAgain: true,
      expires: "never",
    });
    notifications.getExpoPushTokenAsync.mockResolvedValue({
      data: "ExponentPushToken[abc]",
      type: "expo",
    });
 
    await expect(registerForPushNotifications()).resolves.toBe(
      "ExponentPushToken[abc]"
    );
    expect(notifications.requestPermissionsAsync).not.toHaveBeenCalled();
  });
 
  test("requests permission when not yet granted", async () => {
    notifications.getPermissionsAsync.mockResolvedValue({
      status: "undetermined",
      granted: false,
      canAskAgain: true,
      expires: "never",
    });
    notifications.requestPermissionsAsync.mockResolvedValue({
      status: "granted",
      granted: true,
      canAskAgain: true,
      expires: "never",
    });
    notifications.getExpoPushTokenAsync.mockResolvedValue({
      data: "ExponentPushToken[xyz]",
      type: "expo",
    });
 
    await expect(registerForPushNotifications()).resolves.toBe(
      "ExponentPushToken[xyz]"
    );
    expect(notifications.requestPermissionsAsync).toHaveBeenCalledTimes(1);
  });
 
  test("throws when permission denied", async () => {
    notifications.getPermissionsAsync.mockResolvedValue({
      status: "denied",
      granted: false,
      canAskAgain: false,
      expires: "never",
    });
 
    await expect(registerForPushNotifications()).rejects.toThrow(
      "Push permission denied"
    );
  });
 
  test("returns null on simulator", async () => {
    device.isDevice = false;
 
    await expect(registerForPushNotifications()).resolves.toBeNull();
    expect(notifications.getPermissionsAsync).not.toHaveBeenCalled();
  });
});

What this demonstrates:

jest.mock("expo-*") - replaces the module with auto-mocked functions you configure per test.
jest.mocked() - typed access to mock implementations in TypeScript.
Service-layer tests - native calls isolated in one module; UI tests mock the service instead of three Expo packages.
Explicit permission branches - each status (granted, denied, undetermined) gets its own test.
jest.clearAllMocks() in beforeEach - prevents call-count leakage between tests.

Deep Dive

How It Works

jest-expo preset installs default mocks for Expo modules so imports do not crash Jest. Defaults return resolved promises with generic "success" shapes - rarely matching your production edge cases.
jest.mock("module-name") hoists to the top of the file and swaps the module before your imports evaluate. Works for expo-*, @react-native-async-storage/async-storage, and app-local modules.
Manual mocks in __mocks__/ next to node_modules package name or src/ file apply when you call jest.mock without a factory.
Spy pattern - jest.spyOn(module, "fn") wraps a single function while leaving the rest real (when not fully mocked).
Boundary mocking - mock src/services/api.ts, not fetch and not every transitive import, unless testing the HTTP client itself.

What jest-expo Mocks vs What You Must Mock

Category	jest-expo default	You override when
`expo-constants`, `expo-font`	Safe stubs	App reads specific `extra` config values
`expo-location`, `expo-camera`	Generic granted/success	Testing denial, timeout, or sensor errors
`expo-notifications`	Basic async fns	Permission flows and token shapes
Custom native module	Not mocked	Always - provide manual mock or wrapper
Third-party RN SDK (analytics, ads)	Not mocked	Mock at import site or facade module

Manual Mock Patterns

Inline factory (per test file):

jest.mock("expo-secure-store", () => ({
  getItemAsync: jest.fn(),
  setItemAsync: jest.fn(),
  deleteItemAsync: jest.fn(),
}));

Shared manual mock file:

src/
  services/
    analytics.ts
  __mocks__/
    analytics.ts      # manual mock - jest.mock("../services/analytics") picks it up

// src/__mocks__/analytics.ts
export const trackEvent = jest.fn();
export const identifyUser = jest.fn();

Re-export real module with one spy:

jest.mock("expo-linking", () => {
  const actual = jest.requireActual<typeof import("expo-linking")>("expo-linking");
  return {
    ...actual,
    openURL: jest.fn(actual.openURL),
  };
});

Avoiding False Confidence

Passing Jest test	Still verify on device
Mocked camera returns a URI	Real camera permissions and capture pipeline
Mocked biometrics always succeeds	Face ID / fingerprint failure UI
Mocked push token string	APNs/FCM registration on physical hardware
Mocked deep link URL	OS opening the app from cold start

Treat Jest native mocks as contract tests for your JS reaction - not proof the native bridge works. Add Maestro E2E or manual QA for permission dialogs and hardware paths.

TypeScript Notes

import type { LocationObject } from "expo-location";
 
function buildLocation(overrides: Partial<LocationObject> = {}): LocationObject {
  return {
    coords: {
      latitude: 0,
      longitude: 0,
      altitude: 0,
      accuracy: 0,
      altitudeAccuracy: 0,
      heading: 0,
      speed: 0,
    },
    timestamp: Date.now(),
    ...overrides,
  };
}
 
mockLocation.getCurrentPositionAsync.mockResolvedValue(
  buildLocation({ coords: { latitude: 51.5, longitude: -0.12, altitude: 0, accuracy: 1, altitudeAccuracy: 1, heading: 0, speed: 0 } })
);

Import types from the real package even when the implementation is mocked.
Use jest.mocked(fn) instead of (fn as jest.Mock) for stricter typing.
Factory mocks can call jest.requireActual to preserve unmocked exports and reduce drift.

Gotchas

Assuming jest-expo defaults match your test - Default permission mocks often return granted. Tests never exercise denial paths unless you override. Fix: Set mockResolvedValue for each permission/status scenario explicitly.
Mocking too deep - Mocking react-native internals or every expo-* import makes tests brittle when SDK updates changes signatures. Fix: Mock your service boundary; keep one module responsible for native calls.
Forgetting jest.clearAllMocks() - Call counts and queued implementations leak across tests. Fix: afterEach in jest.setup.ts or beforeEach in describe blocks that use spies.
jest.requireActual after full mock - Spreading requireActual for native modules can pull real native bindings into Jest and crash. Fix: Mock only the functions you call; avoid requireActual on modules that touch native code.
False confidence from green suites - All native behavior faked; production still fails on a real device. Fix: Document which flows need Maestro or manual device checks in PR templates.
Dynamic import() bypassing mocks - Lazy imports may resolve before jest.mock applies if mis-ordered. Fix: Use static imports in code under test, or jest.unstable_mockModule for ESM dynamic import paths.
Duplicating mock setup in every file - Copy-pasted expo-font mocks drift. Fix: Shared helpers in test-utils/native-mocks.ts or global mocks in jest.setup.ts for app-wide modules (fonts, splash screen).

Alternatives

Alternative	Use When	Don't Use When
`jest-expo` auto-mocks	Default - module imports should not crash Jest	You need realistic permission denial without overrides
Inline `jest.mock` factory	Per-test-file control of return values	Same mock repeated in 20 files - extract a helper
`__mocks__/` manual files	Shared mock across many tests	One-off behavior only used once
Service facade + mock facade	Clean architecture, swappable implementations	Throwaway prototype with no service layer
Maestro / Detox on device	Real OS permissions and native UI	Fast feedback on pure logic branches
`@shopify/react-native-skia` mock community packages	Heavy native deps with published Jest shims	Expo modules already covered by `jest-expo`

FAQs

Does jest-expo mock every Expo module?

It mocks the majority of expo-* packages shipped with the SDK. Custom native modules, bare third-party SDKs, and some community packages are not covered - add jest.mock manually.

Where do I put shared mocks?

App-wide: jest.setup.ts (fonts, splash screen, constants).
Feature-specific: top of the test file or __tests__/helpers/.
Package-style: __mocks__/expo-location.ts at project root for jest.mock("expo-location") auto-resolution.

jest.mock vs jest.spyOn?

jest.mock replaces the entire module - use for native bridges.
jest.spyOn wraps one method - use when most of the module should stay real (rare with native modules in Jest).

How do I mock AsyncStorage?

jest.mock("@react-native-async-storage/async-storage", () =>
  require("@react-native-async-storage/async-storage/jest/async-storage-mock")
);

The package ships an official Jest mock - prefer it over hand-rolled key-value objects.

How do I mock expo-router?

Prefer renderRouter from expo-router/testing-library over mocking useRouter when testing navigation. For leaf components, pass navigation callbacks as props instead of mocking the router hook.

Can I mock only one function in a module?

jest.mock("expo-linking", () => ({
  ...jest.requireActual("expo-linking"),
  openURL: jest.fn(() => Promise.resolve(true)),
}));

Use sparingly - requireActual on native-heavy modules can fail; a thin wrapper module is safer.

Why does my mock not apply?

jest.mock must be at module scope (hoisted), not inside it/beforeEach.
Ensure the import path matches exactly what production code imports.
Clear Metro/Jest cache: npx jest --clearCache.

Should I mock fetch or the API client?

Mock src/api/client or the TanStack Query queryFn wrapper - not both. One boundary keeps tests focused on how the app handles success and error responses.

How do I simulate permission denial?

mockLocation.requestForegroundPermissionsAsync.mockResolvedValue({
  status: "denied",
  granted: false,
  canAskAgain: false,
  expires: "never",
});

Match the shape from the real Expo module's TypeScript types - incomplete objects cause false positives.

What is false confidence?

Tests pass because mocks always return success, while real users hit denial dialogs, airplane mode, or OS bugs. Complement Jest with Maestro E2E for permission and OS-integration paths.

How do I test a custom Expo native module?

Do mocks belong in setupFilesAfterEnv?

Only for modules every test needs (fonts, splash, reanimated silence). Feature mocks belong next to the tests that assert on them - global mocks hide missing setup in new tests.

How do I reset mocks between tests?

afterEach(() => {
  jest.clearAllMocks(); // clears call history
  // jest.resetAllMocks(); // also resets implementations - use when tests override mockResolvedValue
});

Add to jest.setup.ts for project-wide consistency.

Jest Setup for Expo - jest-expo preset and global setup
React Native Testing Library - assert UI after mocks resolve
Mobile Testing Basics - what belongs in unit vs E2E layers
Maestro E2E - real device flows mocks cannot replace
Expo Modules Core - how native modules expose JS APIs
Native Modules Basics - custom bridges that always need manual mocks

Stack versions: This page was written for React 19.2.3, React Native 0.86.0, and Expo SDK 57 (expo ~57.0.4).

Mocking Native Modules

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Mocking Native Modules