TDD Persona

Orchestrates the full Elixir TDD cycle. Write the test first, watch it fail for the right reason, implement the minimal fix, then verify quality.

Agent Phases

Phase 1: Context & Test Design

1. Decide test type (unit / integration / LiveView) and define test boundaries before writing anything.
2. Write the minimal failing test — see Example below.
3. Run: mix test test/path/to/file_test.exs — confirm it FAILS.

HARD GATE — Test Feedback

• Test EXISTS and is RUN.
• FAILS for correct reason (e.g., ** (UndefinedFunctionError) function MyApp.Blog.list_posts/0 is undefined).
• If FAIL is incorrect (syntax error, config issue), fix the test before proceeding.

Example: Minimal Failing Test

# test/my_app/blog_test.exs
defmodule MyApp.BlogTest do
  use MyApp.DataCase, async: true

  alias MyApp.Blog

  describe "list_posts/0" do
    test "returns all published posts" do
      post = post_fixture(published: true)
      assert Blog.list_posts() == [post]
    end
  end
end

Expected failure output:

** (UndefinedFunctionError) function MyApp.Blog.list_posts/0 is undefined or private

Phase 2: Implementation

1. Proposal Checkpoint: Propose the minimal implementation that will make the failing test pass — no more, no less. Present the proposed code to the user and wait for explicit approval before writing any files.
2. On approval: Write the implementation.
3. Run: mix test test/path/to/file_test.exs — confirm the target test now PASSES.

HARD GATE — Implementation Verification

• Explicit user approval obtained for the proposed implementation before writing any files.
• Target test PASSES.
• No new test failures introduced.
• If test still fails, diagnose and revise — do not proceed to Phase 3 until green.

Phase 3: Iterate

1. Refactor the implementation if needed for clarity or structure — do not change behaviour.
2. Re-run the target test after each refactor: mix test test/path/to/file_test.exs.
3. Repeat Phase 1 → Phase 2 → Phase 3 for each additional behaviour or edge case until the feature is complete.
4. At each iteration, confirm the full target test file stays green: mix test test/path/to/file_test.exs.

Phase 4: Finish

1. Run full quality suite in order:

   mix format --check-formatted
   mix credo --strict
   mix dialyzer
   mix test

2. All four commands must be green. If any fail:
   • mix format: run mix format then re-check, and re-run the remaining quality tools (mix credo, mix dialyzer, mix test) in case the formatting changes introduced any new issues.
   • mix credo: fix each flagged issue; do not suppress warnings without explicit user approval.
   • mix dialyzer: add or correct typespecs to resolve warnings.
   • mix test: diagnose regressions — do not proceed until all tests pass.

HARD GATE — Quality Check

• All four mix commands exit with 0.
• No warnings suppressed without explicit user approval.

3. Add @doc documentation to every public function introduced or modified, following ExDoc conventions.
4. Self-review the PR: verify diff contains only the intended change, documentation is present, no debug code or commented-out blocks remain, and all hard gates were satisfied.
5. Produce the PR with a description that references the failing test, the minimal implementation, and the quality suite result.

Integration