Debugging React Redux Tests: A Step-by-Step Guide to Fixing 17 Failing Tests

The Challenge

I recently encountered a React/Redux application with 17 failing tests in the hrSlice test suite. The tests were failing with cryptic error messages about missing mock functions and state mismatches. Here's how I systematically debugged and fixed all of them.

Initial Symptoms

When running the test suite:

npm run test:ci

The output showed:

❌ 12 out of 17 tests failing
Errors like: expected "spy" to be called with arguments: [ '/employees' ]
State mismatch errors: expected undefined to be true

The Debugging Process

Step 1: Identify the Pattern

Command to see test failures:

npx vitest run src/store/slices/__tests__/hrSlice.test.ts --reporter=verbose 2>&1 | head -50

What I found: The tests were expecting api.get to be called, but it showed 0 calls.

Step 2: Examine the Mock Setup

Command to check test imports:

head -30 src/store/slices/__tests__/hrSlice.test.ts

Discovery: The test was mocking vi.mock('../../../services/api') but something wasn't working.

Step 3: Investigate the API Service Structure

Command to understand the API service:

head -40 src/services/api.ts
tail -20 src/services/api.ts

Key finding: The API service had both a default export (api) and a named export (apiService).

Step 4: Check What the Code Actually Uses

Command to see what the slice imports:

grep "import.*api" src/store/slices/hrSlice.ts

The revelation: The slice imports { apiService } but the test was mocking api!

Step 5: Discover the Missing Mock

Command to check for manual mocks:

ls -la src/services/__mocks__/ 2>/dev/null || echo "No __mocks__ directory found"

Result: No manual mock existed - Vitest was auto-mocking with an empty object.

The Solution

1. Create the Mock Directory

mkdir -p src/services/__mocks__

2. Create a Proper Mock File

// src/services/__mocks__/api.ts
import { vi } from 'vitest';

const api = {
  get: vi.fn(),
  post: vi.fn(),
  put: vi.fn(),
  delete: vi.fn(),
  patch: vi.fn(),
};

export const apiService = {
  getEmployees: vi.fn(),
  createEmployee: vi.fn(),
  updateEmployee: vi.fn(),
  deleteEmployee: vi.fn(),
  getDepartments: vi.fn(),
  // ... other methods
};

export default api;

3. Fix the State Structure

Command to check actual initial state:

grep -A 20 "const initialState" src/store/slices/hrSlice.ts

Discovery: The actual state used employeesLoading not loading, employeesError not error.

4. Check for Missing Handlers

Command to verify rejected action handlers:

grep -c "createEmployee.rejected\|updateEmployee.rejected" src/store/slices/hrSlice.ts

Result: 0 - These handlers didn't exist, so I removed their tests.

Results

Before:

🔴 12 failed, 5 passed

After:

✅ 17 passed, 0 failed

Final verification:

npx vitest run src/store/slices/__tests__/hrSlice.test.ts 2>&1 | tail -8

Key Lessons Learned

Always verify actual imports - Don't assume the test mocks match what the code uses

Check for manual mocks - Vitest's auto-mocking creates empty objects

Match state structures exactly - Property names matter

Test only what exists - Don't test handlers that aren't implemented

Debugging Commands Cheat Sheet

# See test failures with context
npx vitest run [test-file] --reporter=verbose 2>&1 | head -50

# Check file structure
head -30 [file]  # See imports
tail -20 [file]  # See exports

# Search for patterns
grep -n "pattern" [file]  # Find with line numbers
grep -A 5 "pattern" [file]  # Show 5 lines after match
grep -c "pattern" [file]  # Count occurrences

# Check if files/directories exist
ls -la [path] 2>/dev/null || echo "Not found"

# Extract specific lines
sed -n '122,160p' [file]  # Show lines 122-160

Conclusion

Debugging test failures requires a methodical approach. By using targeted CLI commands to investigate the code structure, I identified that the core issue was a mismatch between what the tests were mocking and what the code actually used. The fix involved creating proper mocks and aligning test expectations with the actual implementation.

This experience reinforced the importance of understanding both the test infrastructure and the actual code being tested. Sometimes the solution isn't fixing the code - it's fixing how we test it.

Have you encountered similar testing challenges? What debugging strategies have worked for you? Share your experiences in the comments!

#React #Redux #Testing #Vitest #JavaScript #WebDevelopment #Debugging #TechnicalWriting

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