Quick Solution Overview
Encountering a TypeError: Cannot redefine property x
error in Jest tests can be resolved using two main approaches:
Approach 1: Using jest.mock
Mock the module directly:
import yourModule from "@/path/to/yourModule";
// ๐ Mock the module
jest.mock("@/path/to/yourModule");
Approach 2: Using Barrel Imports
Re-export functions from a new file:
// chakra.ts
import { useColorMode } from "@chakra-ui/react";
const chakra = {
// ๐ Re-export the function
useColorMode,
};
export default chakra;
Then, mock the function in your test file:
// your.spec.ts
import chakra from "./chakra";
const useColorModeMock = jest.spyOn(chakra, "useColorMode");
useColorModeMock.mockReturnValue({ colorMode: "light" });
Understanding the Problem
The error typically arises when attempting to mock a function that's directly exported from a package. This is common with certain npm packages, like @chakra-ui/react
, where redefining properties directly can trigger a TypeError
.
Example Error Scenario
Here's an example error encountered while testing Risedle Interface:
TypeError: Cannot redefine property: useColorMode
The error occurred when trying to mock useColorMode
from @chakra-ui/react
directly:
import chakra from "@chakra-ui/react";
const useColorModeMock = jest.spyOn(chakra, "useColorMode");
useColorModeMock.mockReturnValue({ colorMode: "light" });
Detailed Solutions
Solution 1: Using jest.mock
Mocking the entire module is straightforward and usually the quickest fix:
import yourModule from "@/path/to/yourModule";
jest.mock("@/path/to/yourModule");
Solution 2: Using Barrel Imports
Create a New File for Re-exports:
Example
chakra.ts
:import { useColorMode } from "@chakra-ui/react"; const chakra = { useColorMode, }; export default chakra;
Mock in Test Files:
In your test file (
your.spec.ts
):import chakra from "./chakra"; const useColorModeMock = jest.spyOn(chakra, "useColorMode"); useColorModeMock.mockReturnValue({ colorMode: "light" });
Conclusion
Both methods effectively solve the "TypeError: Cannot redefine property: x" issue in Jest. The choice depends on your specific testing scenario and preferences. Happy testing!