Jest Coverage Directory Configuration

This challenge focuses on configuring Jest to generate code coverage reports in a specific directory. Properly configured coverage reports are essential for understanding the thoroughness of your test suite and identifying areas that need more testing.

Problem Description

Your task is to configure Jest, a popular JavaScript testing framework, to output its code coverage reports into a custom directory instead of the default location. You will need to modify the Jest configuration file to achieve this.

What needs to be achieved:

• Jest should generate code coverage reports.
• The generated coverage reports must be placed in a directory named custom-coverage at the root of your project.

Key requirements:

• Use TypeScript for your project.
• Ensure Jest is configured to run tests and generate coverage.
• Modify the Jest configuration to point the coverage directory to custom-coverage.

Expected behavior: When you run the Jest command with coverage enabled (e.g., jest --coverage), a directory named custom-coverage should be created in your project's root. Inside this directory, you will find the HTML, JSON, and LCOV coverage reports.

Edge cases to consider:

• What happens if the custom-coverage directory already exists? (Jest should overwrite or update its contents).
• What if no tests are found? (Coverage report generation should still attempt to run, but may be empty or indicate no tests were run).

Examples

Example 1: Assume you have a project with the following structure:

my-project/
├── src/
│   └── index.ts
├── tests/
│   └── index.test.ts
├── package.json
└── jest.config.ts

And jest.config.ts contains a basic Jest configuration.

Input (Command to run):

npm test -- --coverage
# or
yarn test --coverage

Expected Output (Directory Structure after running the command):

my-project/
├── src/
│   └── index.ts
├── tests/
│   └── index.test.ts
├── custom-coverage/  <-- This directory should be created
│   ├── index.html
│   ├── coverage.json
│   └── lcov.info
├── package.json
└── jest.config.ts

Explanation: By configuring Jest correctly, running the coverage command generates the reports within the newly created custom-coverage directory.

Example 2: If jest.config.ts is not yet configured for coverage output directory:

Input (Content of jest.config.ts):

import type { JestConfigWithTsJest } from 'ts-jest';

const config: JestConfigWithTsJest = {
  preset: 'ts-jest',
  testEnvironment: 'node',
};

export default config;

Command to run:

npm test -- --coverage

Expected Output (Directory Structure after running the command): A coverage directory (Jest's default) would be created, not custom-coverage. This is the behavior we aim to change.

Constraints

• Your project must be set up to use TypeScript and Jest.
• The Jest configuration file should be named jest.config.ts.
• The custom coverage directory must be named exactly custom-coverage.
• The solution should focus solely on the Jest configuration. Assume Jest and ts-jest are already installed and functional.

Notes

• You will need to consult the Jest documentation for configuration options related to code coverage.
• Pay close attention to the coverageDirectory option within the Jest configuration.
• Ensure your package.json has a test script that runs Jest with the --coverage flag, or you can invoke Jest directly with this flag.