Add test implementation

.dagger/prompts/assignment.md

@@ -12,6 +12,16 @@ You are a programmer working on the Greetings API project
 
 Here is your assignment: $assignment
 
+## Documentation Best Practices
+
+When creating new documentation files:
+- **Cross-reference related documents**: Add notes linking to other relevant documentation (e.g., CONTRIBUTING.md, README.md) to improve discoverability
+- **Verify accuracy**: Ensure all file paths, function names, and technical details match the actual codebase
+- **Be precise with test coverage**: Only claim test coverage for scenarios that are actually tested in the test files
+- **Avoid circular dependencies**: When providing guidance about updating documentation, be specific about when updates are needed (e.g., "when adding new test files or significantly changing test structure" rather than "when adding new test scenarios")
+- **Include practical examples**: Provide clear command-line examples for common operations
+- **Consider the audience**: Write for both new and existing contributors
+
 ## Constraints
 - You have access to a workspace with the code and the tests
 - The workspace has tools to let you read and write the code as well as run the tests

TESTING.md

@@ -0,0 +1,118 @@
+# Test Documentation
+
+> **Note**: For general contribution guidelines including testing requirements, see [CONTRIBUTING.md](./CONTRIBUTING.md)
+
+This document describes the comprehensive testing approach for the Greetings API project.
+
+## Overview
+
+The Greetings API project includes multiple layers of testing to ensure reliability and correctness:
+- Unit tests for backend logic
+- End-to-end tests for the frontend
+- Linting for code quality
+
+## Backend Tests
+
+The backend tests are located in `main_test.go` and use the `gotest.tools/v3` testing framework.
+
+### Test Functions
+
+#### TestSelectGreeting
+Tests the core greeting selection logic with multiple scenarios:
+- **Valid language selection**: Tests retrieval of greetings by specific language (e.g., "english")
+- **Random selection**: Tests the random greeting functionality
+- **Invalid language handling**: Verifies proper error handling for non-existent languages
+- **Empty language handling**: Ensures errors are returned for empty language strings
+
+#### TestFormatResponse
+Tests the JSON response formatting:
+- Verifies the greeting is properly formatted as JSON
+- Ensures the structure matches the expected API response format: `{"greeting":"<message>"}`
+
+### Test Coverage
+
+Current test coverage includes:
+- ✅ Greeting selection by language
+- ✅ Random greeting selection  
+- ✅ Error handling for invalid languages
+- ✅ Error handling for empty language strings
+- ✅ Response formatting
+
+## Frontend Tests
+
+End-to-end tests for the frontend are located in `website/cypress/e2e/greeting_test.cy.ts` using Cypress.
+
+### Test Scenarios
+
+1. **Page Load Test**: Verifies the page loads correctly with the expected header
+2. **Greeting Button Test**: Verifies clicking the greeting button changes the displayed message
+
+## Running Tests
+
+### All Tests (Recommended)
+```bash
+dagger call check
+```
+
+This runs:
+- Backend linting (golangci-lint)
+- Backend unit tests
+- Frontend E2E tests
+- Frontend linting
+
+### Backend Tests Only
+```bash
+# Using Dagger
+dagger call test
+
+# Or directly with Go
+go test ./...
+```
+
+### Frontend Tests Only
+```bash
+cd website
+npm run test:e2e
+```
+
+### Linting Only
+```bash
+# Backend
+dagger call lint
+
+# Frontend (part of check command)
+dagger call check
+```
+
+## Test Data
+
+Greetings test data is embedded from `greetings.json` which includes:
+- 17 different language greetings
+- Languages: English, British, French, Italian, Spanish, German, Mandarin, Hindi, Arabic, Bengali, Russian, Portuguese, Urdu, Indonesian, Japanese, Marathi, Telugu
+
+## Continuous Integration
+
+Tests are automatically run in CI through Dagger modules. The CI ensures:
+- All tests pass before merging
+- Code meets linting standards
+- No regressions are introduced
+
+## Future Test Improvements
+
+Potential areas for additional testing coverage:
+- HTTP handler integration tests (testing the actual HTTP endpoints with httptest)
+- Additional edge cases for error handling
+- Performance/load testing for the API
+- Testing CORS functionality
+- Testing with empty greetings.json
+- Concurrency testing for random selection
+
+## Test Best Practices
+
+When adding new tests:
+1. Follow Go testing conventions
+2. Use descriptive test function names
+3. Test both happy paths and error cases
+4. Keep tests isolated and independent
+5. Run `dagger call check` before committing
+6. Update TESTING.md when adding new test files or significantly changing test structure