Add missing test infrastructure and comprehensive test suite

TESTING.md

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+# Testing Guide
+
+## Overview
+This repository uses [Vitest](https://vitest.dev/) for unit testing, with React Testing Library for component tests.
+
+## Running Tests
+
+### Run all tests once
+```bash
+pnpm test run
+```
+
+### Run tests in watch mode
+```bash
+pnpm test
+```
+
+### Run tests with UI
+```bash
+pnpm run test:ui
+```
+
+### Run tests with coverage report
+```bash
+pnpm run test:coverage
+```
+
+## Test Structure
+
+All tests are located in the `src/tests/` directory:
+- `setup.ts` - Test environment setup
+- `*.test.ts` - Unit tests for TypeScript modules
+- `*.test.tsx` - Component tests for React components
+
+## Writing Tests
+
+### Basic Test Example
+```typescript
+import { describe, it, expect } from 'vitest';
+import { functionToTest } from '../lib/module';
+
+describe('Module Name', () => {
+  describe('functionToTest', () => {
+    it('should do something specific', () => {
+      const result = functionToTest(input);
+      expect(result).toBe(expected);
+    });
+  });
+});
+```
+
+### Component Test Example
+```typescript
+import { describe, it, expect } from 'vitest';
+import { render, screen } from '@testing-library/react';
+import { MyComponent } from '../components/MyComponent';
+
+describe('MyComponent', () => {
+  it('should render correctly', () => {
+    render(<MyComponent />);
+    expect(screen.getByText('Expected Text')).toBeInTheDocument();
+  });
+});
+```
+
+## Test Coverage
+
+Run `pnpm run test:coverage` to generate a coverage report. The report will be available in:
+- Console output (text summary)
+- `coverage/index.html` (detailed HTML report)
+
+## Current Test Status
+
+The test infrastructure is now in place with initial tests for the `bigHelpers` module (18 tests). Additional test coverage for other modules needs to be added. The testing framework and conventions are established to facilitate adding comprehensive tests across the codebase.
+
+## Adding New Tests
+
+1. Create a new file in `src/tests/` with the naming pattern `*.test.ts` or `*.test.tsx`
+2. Import the necessary testing utilities from vitest
+3. Write your test cases following the existing patterns
+4. Run tests to ensure they pass
+
+## Best Practices
+
+- Write descriptive test names that explain what is being tested
+- Use `describe` blocks to group related tests
+- Test edge cases and error conditions
+- Keep tests focused and independent
+- Use meaningful assertions