Instruction file imported from nestorrd/python-ai-assisted-dev-sample (.github/instructions/app.instructions.md). Copyright stays with the author.

applyTo: "app/*.py"

Development Workflow for App Code

When adding or modifying any code in app/, always follow the TDD (Test-Driven Development) workflow using the tdd-python skill.

Mandatory TDD Requirement

No production code may be written without a failing test first. For every new function, class, or behaviour:

1. Invoke the tdd-python skill and follow its Red-Green-Refactor cycle exactly.
2. Write the failing test in tests/ before touching any file in app/.
3. Only write the minimum production code needed to make the test pass.
4. Refactor only when all tests are green.

Coverage Goals

• Aim for 100% line and branch coverage of all code in app/.
• Every public function and every code branch (including error paths, edge cases, and guard clauses) must have at least one dedicated test.
• After implementing a feature, run pytest --cov=app --cov-branch --cov-report=term-missing and address any uncovered lines before considering the work done.

What Must Be Tested

• Happy paths: typical valid inputs producing expected outputs.
• Error paths: invalid inputs, missing files, malformed data — anything that raises an exception or returns an error.
• Edge cases: empty inputs, zero values, boundary conditions.
• All branches: every if/elif/else and try/except block.

Workflow Summary

1. Read the requirement.
2. List all behaviours as bullet points.
3. For each behaviour → run one full Red-Green-Refactor cycle (tdd-python skill).
4. After all cycles → run pytest --cov=app --cov-branch --cov-report=term-missing.
5. For any uncovered line → add a test and repeat the cycle.