Jest Path Coverage Challenge

This challenge focuses on achieving full path coverage in your Jest tests. Path coverage ensures that every possible branch and execution path within your code is executed at least once during testing. This is crucial for uncovering subtle bugs that might be missed with simpler coverage metrics.

Problem Description

You are tasked with writing Jest tests for a given TypeScript function. The goal is to ensure that your test suite achieves 100% path coverage for this function. This means designing tests that exercise every possible execution path, including conditional branches, loops, and error handling.

What needs to be achieved: Write a Jest test suite for the provided processUserData function that achieves 100% path coverage.

Key requirements:

1. Write tests in TypeScript.
2. Use Jest as the testing framework.
3. Achieve 100% path coverage for the processUserData function.
4. Cover all conditional branches (e.g., if, else if, else, ternary operators).
5. Cover different loop scenarios (if applicable).
6. Test error handling and edge cases.

Expected behavior: Your tests should demonstrate that each distinct execution path within processUserData is executed. When running Jest with coverage reporting (e.g., jest --coverage), the report should indicate 100% path coverage for the processUserData function.

Important edge cases to consider:

• Empty or null inputs.
• Invalid input types.
• Specific values that trigger different conditional branches.
• Scenarios that might lead to errors or exceptions.

Examples

Let's consider a simplified example function to illustrate the concept of path coverage.

Example Function:

// src/utils.ts
export function determineUserStatus(user: { isActive: boolean; isAdmin: boolean }): string {
  if (user.isActive) {
    if (user.isAdmin) {
      return "Active Admin";
    } else {
      return "Active User";
    }
  } else {
    return "Inactive User";
  }
}

Target: Achieve 100% path coverage for determineUserStatus.

Explanation of Paths:

1. user.isActive is true, user.isAdmin is true -> "Active Admin"
2. user.isActive is true, user.isAdmin is false -> "Active User"
3. user.isActive is false -> "Inactive User"

Example Test Case (Illustrative - you will write tests for the actual problem function):

// src/utils.test.ts
import { determineUserStatus } from './utils';

describe('determineUserStatus', () => {
  test('should return "Active Admin" for an active admin user', () => {
    const user = { isActive: true, isAdmin: true };
    expect(determineUserStatus(user)).toBe('Active Admin');
  });

  test('should return "Active User" for an active non-admin user', () => {
    const user = { isActive: true, isAdmin: false };
    expect(determineUserStatus(user)).toBe('Active User');
  });

  test('should return "Inactive User" for an inactive user', () => {
    const user = { isActive: false, isAdmin: true }; // isAdmin doesn't matter if inactive
    expect(determineUserStatus(user)).toBe('Inactive User');
  });
});

This test suite would achieve 100% path coverage for the determineUserStatus function.

The Function to Test

You will be writing tests for the following TypeScript function:

// src/processUserData.ts
export function processUserData(user: { id: number; name: string; email?: string; role: 'user' | 'admin' | 'guest'; preferences?: { theme: string; notifications: boolean } }): { status: string; message: string; userId: number } | { error: string } {
  if (!user || typeof user.id !== 'number' || typeof user.name !== 'string' || !user.role) {
    return { error: "Invalid user data provided." };
  }

  let status = "Processing";
  let message = `User ${user.name} (ID: ${user.id}) is being processed.`;

  if (user.role === 'admin') {
    status = "Admin";
    message += " This user has administrative privileges.";
    if (user.email) {
      message += ` Admin email: ${user.email}`;
    }
  } else if (user.role === 'guest') {
    status = "Guest";
    message = `Guest ${user.name} (ID: ${user.id}) has limited access.`;
    if (!user.email) {
      message += " No email provided for guest.";
    }
  } else { // user.role === 'user'
    status = "Standard User";
    message += " This is a standard user account.";
    if (user.preferences) {
      message += ` Theme preference: ${user.preferences.theme}.`;
      if (user.preferences.notifications) {
        message += " Notifications are enabled.";
      } else {
        message += " Notifications are disabled.";
      }
    }
  }

  // Simulate some additional processing that might throw an error
  if (user.id < 0) {
    throw new Error("User ID cannot be negative.");
  }

  return { status, message, userId: user.id };
}

Constraints

• The provided processUserData function in src/processUserData.ts is the target.
• Your tests must be written in TypeScript and placed in a src/processUserData.test.ts file.
• You must use Jest for testing.
• The primary goal is to achieve 100% path coverage for the processUserData function.
• Focus on covering all logical branches and execution flows.
• Do not modify the processUserData function itself.

Notes

• Use Jest's built-in assertion library (expect).
• When running jest --coverage, observe the output to confirm 100% path coverage for processUserData.
• Think carefully about the different combinations of input properties that will lead to unique execution paths.
• Consider what values for user.role, user.email, user.preferences, and user.id will trigger different parts of the conditional logic.
• Pay attention to the initial validation checks and the potential error thrown at the end.
• A good strategy is to map out the possible paths manually before writing tests. For example:
  • Path 1: Invalid data (e.g., missing ID)
  • Path 2: Valid data, role is 'admin', has email
  • Path 3: Valid data, role is 'admin', no email
  • Path 4: Valid data, role is 'guest', has email
  • Path 5: Valid data, role is 'guest', no email
  • Path 6: Valid data, role is 'user', has preferences, theme="dark", notifications=true
  • Path 7: Valid data, role is 'user', has preferences, theme="light", notifications=false
  • Path 8: Valid data, role is 'user', no preferences
  • Path 9: Valid data, ID is negative (throws error)
  • Path 10: Valid data, ID is non-negative (successful return)
  • And so on... cover all combinations!