Jest AST Transformation: Replacing Console Logs with Mock Functions

This challenge focuses on creating a Jest test utility that automatically transforms the Abstract Syntax Tree (AST) of your JavaScript/TypeScript code to replace console.log calls with calls to mock functions. This is incredibly useful for suppressing console output during tests, preventing noisy test results and potential side effects from logging. You'll be leveraging the babel-plugin-transform-remove-console library and Jest's transform option to achieve this.

Problem Description

You need to create a Jest configuration that automatically replaces all console.log statements within your test files with calls to a mock function. This mock function should be defined within your test file and will be used to capture and assert on the logged messages. The transformation should be applied only to test files, leaving your production code untouched. The goal is to provide a clean and reliable way to test code that relies on console.log for debugging or informational purposes, without polluting the test output.

Key Requirements:

• AST Transformation: Utilize a Babel plugin (babel-plugin-transform-remove-console) to modify the AST of your test files.
• Mock Function Generation: The transformation should replace console.log calls with calls to a mock function defined within the test file. The mock function should accept the same arguments as the original console.log call.
• Selective Application: The transformation should only be applied to files matching a specific glob pattern (e.g., *.test.ts, *.spec.ts).
• Jest Integration: Integrate the transformation seamlessly into your Jest configuration.
• TypeScript Support: The solution must work correctly with TypeScript files.

Expected Behavior:

When a test file containing console.log statements is executed, the console.log calls will be replaced with calls to a mock function. You can then assert on the arguments passed to the mock function to verify the expected behavior.

Edge Cases to Consider:

• console.log calls within template literals.
• console.log calls with multiple arguments of different types.
• console.log calls within complex expressions.
• Files that don't match the test file glob pattern should not be transformed.
• Ensure the mock function is properly scoped within the test file.

Examples

Example 1:

Input (test.ts):
```typescript
function myFunction(message: string) {
  console.log("Message:", message);
}

myFunction("Hello, world!");

Output (after transformation):
```typescript
function myFunction(message: string) {
  const consoleLogMock = jest.fn();
  consoleLogMock("Message:", message);
}

myFunction("Hello, world!");

Example 2:

Input (test.ts):
```typescript
const name = "Alice";
console.log(`Name: ${name}, Age: 30`);

Output (after transformation):
```typescript
const name = "Alice";
const consoleLogMock = jest.fn();
consoleLogMock(`Name: ${name}, Age: 30`);

Constraints

• Babel Plugin: You must use babel-plugin-transform-remove-console for the AST transformation. Do not attempt to write your own AST transformer.
• Jest Configuration: The solution must be implemented as a Jest configuration file (e.g., jest.config.js, jest.config.ts).
• Glob Pattern: The transformation should be applied to files matching the glob pattern **/*.test.(ts|tsx|js|jsx).
• Performance: The transformation should not significantly impact test execution time. While optimization isn't the primary focus, avoid unnecessarily complex logic.
• Dependencies: You are allowed to use babel-plugin-transform-remove-console and jest. No other external dependencies are permitted.

Notes

• You'll need to configure Jest's transform option to use a Babel preset that includes the babel-plugin-transform-remove-console plugin.
• Consider using a Babel configuration file (babel.config.js or babel.config.ts) to manage your Babel presets and plugins.
• The mock function generated by the transformation should be a jest.fn() to allow for assertions on its calls.
• Think about how to ensure the mock function is defined in the same scope as the code being tested. The transformation should insert the mock function definition before the first console.log call it replaces.
• Debugging AST transformations can be tricky. Use Babel's AST explorer (https://astexplorer.net/) to inspect the AST of your code and understand how the transformation is affecting it.