Automated Affected Tests in Jest

Many projects utilize tools like Nx or Turborepo to manage monorepos and optimize build times by only running tasks that are affected by code changes. This challenge focuses on implementing a mechanism to automatically identify and run only the Jest tests that are affected by a given set of modified files. This is crucial for efficient CI/CD pipelines and faster feedback loops during development.

Problem Description

You are tasked with creating a function getAffectedTests that takes two arguments: a list of modified files (strings) and a mapping of files to Jest test files (object). The function should return a list of Jest test files (strings) that are directly or indirectly affected by the modified files. "Affected" means that a test file is affected if it imports or is imported by a modified file, or if it shares a parent directory with a modified file.

Key Requirements:

• Direct Dependency: A test file is affected if it directly imports a modified file.
• Indirect Dependency: A test file is affected if it imports a file that imports a modified file (recursive).
• Shared Directory: A test file is affected if it resides in the same directory as a modified file (or any of its parent directories).
• No Circular Dependencies: The function should handle circular dependencies gracefully and avoid infinite loops.
• Return Unique Test Files: The function should return a list of unique test files.

Expected Behavior:

The function should accurately identify all affected test files based on the provided modified files and file mapping. It should handle various scenarios, including direct and indirect dependencies, shared directories, and circular dependencies.

Edge Cases to Consider:

• Empty list of modified files.
• Empty file mapping.
• Modified files that are not present in the file mapping.
• Circular dependencies between modified files and test files.
• Deeply nested directory structures.
• Test files importing each other.

Examples

Example 1:

Input: modifiedFiles = ["src/utils/math.ts", "src/components/Button.tsx"], fileMapping = {
  "src/components/Button.tsx": ["src/components/Button.test.tsx", "src/components/Button.spec.tsx"],
  "src/utils/math.ts": ["src/utils/math.test.ts"],
  "src/components/Button.test.tsx": ["src/components/Button.test.tsx"],
}
Output: ["src/components/Button.test.tsx", "src/components/Button.spec.tsx", "src/utils/math.test.ts"]
Explanation: Button.tsx and math.ts are modified. Button.test.tsx and Button.spec.tsx depend on Button.tsx, and math.test.ts depends on math.ts. Therefore, all four test files are affected.

Example 2:

Input: modifiedFiles = ["src/utils/api.ts"], fileMapping = {
  "src/utils/api.ts": ["src/components/UserList.test.tsx"],
  "src/components/UserList.tsx": ["src/utils/api.ts"],
  "src/components/UserList.test.tsx": ["src/components/UserList.test.tsx"]
}
Output: ["src/components/UserList.test.tsx"]
Explanation: api.ts is modified. UserList.test.tsx depends on api.ts. Therefore, UserList.test.tsx is affected.

Example 3: (Edge Case - Circular Dependency)

Input: modifiedFiles = ["src/utils/helper.ts"], fileMapping = {
  "src/utils/helper.ts": ["src/components/MyComponent.test.tsx"],
  "src/components/MyComponent.test.tsx": ["src/utils/helper.ts"]
}
Output: ["src/components/MyComponent.test.tsx"]
Explanation: helper.ts is modified. MyComponent.test.tsx depends on helper.ts.  MyComponent.test.tsx also depends on helper.ts, but the function should avoid infinite loops and return only the directly or indirectly affected tests.

Constraints

• modifiedFiles: An array of strings, where each string represents the path to a modified file.
• fileMapping: An object where keys are file paths (strings) and values are arrays of strings representing the paths to test files that depend on the key file.
• The function must not enter an infinite loop due to circular dependencies.
• The function should return a list of unique test file paths.
• File paths are relative to the project root.
• The maximum number of modified files is 100.
• The maximum number of test files per file in fileMapping is 20.

Notes

• Consider using a graph traversal algorithm (e.g., Depth-First Search) to identify affected test files.
• Implement a mechanism to detect and prevent circular dependencies. A Set can be useful for tracking visited files.
• Pay close attention to the directory structure when determining shared directories. You may need to parse file paths to extract directory information.
• The fileMapping provides a simplified dependency graph. In a real-world scenario, you might need to parse the code to determine dependencies. This challenge assumes the mapping is accurate.
• Focus on correctness and efficiency. While performance is not a primary concern, avoid unnecessary computations.