TDD Red Phase - Write Failing Tests First

# TDD Red Phase - Write Failing Tests First

Focus on writing clear, specific failing tests that describe the desired behaviour from GitHub issue requirements before any implementation exists.

GitHub Issue Integration

Branch-to-Issue Mapping

- **Extract issue number** from branch name pattern: `*{number}*` that will be the title of the GitHub issue

- **Fetch issue details** using MCP GitHub, search for GitHub Issues matching `*{number}*` to understand requirements

- **Understand the full context** from issue description and comments, labels, and linked pull requests

Issue Context Analysis

- **Requirements extraction** - Parse user stories and acceptance criteria

- **Edge case identification** - Review issue comments for boundary conditions

- **Definition of Done** - Use issue checklist items as test validation points

- **Stakeholder context** - Consider issue assignees and reviewers for domain knowledge

Core Principles

Test-First Mindset

- **Write the test before the code** - Never write production code without a failing test

- **One test at a time** - Focus on a single behaviour or requirement from the issue

- **Fail for the right reason** - Ensure tests fail due to missing implementation, not syntax errors

- **Be specific** - Tests should clearly express what behaviour is expected per issue requirements

Test Quality Standards

- **Descriptive test names** - Use clear, behaviour-focused naming like `returnsValidationError_whenEmailIsInvalid_issue{number}` (adapt casing to your language convention)

- **AAA Pattern** - Structure tests with clear Arrange, Act, Assert sections

- **Single assertion focus** - Each test should verify one specific outcome from issue criteria

- **Edge cases first** - Consider boundary conditions mentioned in issue discussions

Test Patterns (Polyglot)

- **JavaScript/TypeScript**: Use **Jest** or **Vitest** with `describe`/`it` blocks and `expect` assertions

- **Python**: Use **pytest** with descriptive function names and `assert` statements

- **Java/Kotlin**: Use **JUnit 5** with **AssertJ** for fluent assertions

- **C#/.NET**: Use **xUnit** or **NUnit** with **FluentAssertions**

- Apply parameterised/data-driven tests for multiple input scenarios from issue examples

- Create shared test utilities for domain-specific validations outlined in issue

Execution Guidelines

1. **Fetch GitHub issue** - Extract issue number from branch and retrieve full context

2. **Analyse requirements** - Break down issue into testable behaviours

3. **Confirm your plan with the user** - Ensure understanding of requirements and edge cases. NEVER start making changes without user confirmation

4. **Write the simplest failing test** - Start with the most basic scenario from issue. NEVER write multiple tests at once. You will iterate on RED, GREEN, REFACTOR cycle with one test at a time

5. **Verify the test fails** - Run the test to confirm it fails for the expected reason

6. **Link test to issue** - Reference issue number in test names and comments

Red Phase Checklist

- [ ] GitHub issue context retrieved and analysed

- [ ] Test clearly describes expected behaviour from issue requirements

- [ ] Test fails for the right reason (missing implementation)

- [ ] Test name references issue number and describes behaviour

- [ ] Test follows AAA pattern

- [ ] Edge cases from issue discussion considered

- [ ] No production code written yet