Jest setupFilesAfterEnv Configuration Challenge

Jest's setupFilesAfterEnv configuration option allows you to run setup code after the test environment has been set up but before tests are run. This is particularly useful for tasks like mocking modules globally, setting up database connections, or initializing global state that should be consistent across all tests. This challenge asks you to create a Jest configuration that utilizes setupFilesAfterEnv to mock a specific module.

Problem Description

You need to configure Jest to mock the axios module globally using setupFilesAfterEnv. The mock should replace all axios methods (e.g., axios.get, axios.post) with functions that return a predefined mock response. The mock response should be a promise resolving to { data: { message: 'Mocked Response' } }. Your solution should involve creating a Jest configuration file (jest.config.ts or jest.config.js) that specifies the setupFilesAfterEnv option pointing to a setup file.

Key Requirements:

• Create a Jest configuration file.
• Define setupFilesAfterEnv to point to a setup file (e.g., src/setupTests.ts).
• Within the setup file, mock the axios module globally.
• The mock should replace all axios methods with a function that returns a promise resolving to { data: { message: 'Mocked Response' } }.
• The mocking should be applied after the test environment is set up.

Expected Behavior:

When a test imports axios and calls any of its methods, the mock function defined in setupFilesAfterEnv should be executed instead of the actual axios implementation. The test should then assert that the response data matches the expected mock response.

Edge Cases to Consider:

• Ensure the mock is applied globally, affecting all tests.
• Handle potential errors during the mocking process gracefully.
• The setup file should execute after the environment is set up, so any environment variables or other setup steps should be completed before mocking.

Examples

Example 1:

// test.ts
import axios from 'axios';

test('should mock axios', async () => {
  const response = await axios.get('/some-url');
  expect(response.data.message).toBe('Mocked Response');
});

Output:

The test should pass, demonstrating that the axios.get call was intercepted by the mock.

Example 2:

// test.ts
import axios from 'axios';

test('should mock axios post', async () => {
  const response = await axios.post('/some-url', { data: 'test' });
  expect(response.data.message).toBe('Mocked Response');
});

Output:

The test should pass, demonstrating that the axios.post call was intercepted by the mock.

Constraints

• The solution must be written in TypeScript.
• The Jest configuration file must be valid and functional.
• The mock should replace all axios methods, not just axios.get.
• The mock response must be a promise resolving to an object with the specified structure: { data: { message: 'Mocked Response' } }.
• The solution should be relatively concise and readable.

Notes

• Consider using jest.mock with the setupFilesAfterEnv option to achieve global mocking.
• Ensure that the setup file is correctly imported and executed by Jest.
• Think about how to handle potential errors during the mocking process. While not strictly required, robust error handling is good practice.
• The goal is to demonstrate the correct usage of setupFilesAfterEnv for global mocking.