Override exported variable in file within __mocks__ folder in jest
When writing tests for your TypeScript code using Jest, you may come across a situation where you need to override an exported variable in a file within the mocks folder. This can be useful when you want to mock a specific behavior or return value for a function or variable.
There are a few different ways to override an exported variable in a file within the mocks folder in Jest. Let’s explore some of these solutions:
Solution 1: Using jest.mock()
The first solution involves using the jest.mock() function to mock the entire module. This allows you to override the exported variable with a custom implementation or value.
Here’s an example:
// myModule.ts
export const myVariable = 'original value';
// __mocks__/myModule.ts
export const myVariable = 'mocked value';
// myModule.test.ts
jest.mock('./myModule'); // This will automatically use the mock implementation
test('should use the mocked value', () => {
const { myVariable } = require('./myModule');
expect(myVariable).toBe('mocked value');
});
Solution 2: Using jest.doMock()
The second solution involves using the jest.doMock() function to mock the specific variable within the module. This allows you to override the exported variable without mocking the entire module.
Here’s an example:
// myModule.ts
export const myVariable = 'original value';
// __mocks__/myModule.ts
export const myVariable = 'mocked value';
// myModule.test.ts
jest.doMock('./myModule', () => {
const originalModule = jest.requireActual('./myModule');
return {
...originalModule,
myVariable: 'mocked value',
};
});
test('should use the mocked value', () => {
const { myVariable } = require('./myModule');
expect(myVariable).toBe('mocked value');
});
Solution 3: Using jest.setMock()
The third solution involves using the jest.setMock() function to set the mock for the specific module. This allows you to override the exported variable with a custom implementation or value.
Here’s an example:
// myModule.ts
export const myVariable = 'original value';
// __mocks__/myModule.ts
export const myVariable = 'mocked value';
// myModule.test.ts
jest.setMock('./myModule', {
myVariable: 'mocked value',
});
test('should use the mocked value', () => {
const { myVariable } = require('./myModule');
expect(myVariable).toBe('mocked value');
});
These are three different solutions you can use to override an exported variable in a file within the mocks folder in Jest. Choose the solution that best fits your specific use case and enjoy seamless testing with Jest and TypeScript!
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