tdd

## When to invoke Use when asked to "do tdd", "red-green-refactor", "test-first development", "build with tdd", or you want integration-style tests that survive refactors. Proactively suggest when starting a new feature or bug fix where the behavior is testable through a public interface. ## Preamble ```bash eval "$(~/.vibestack/bin/vibe-slug 2>/dev/null)" 2>/dev/null || SLUG="unknown" _LEARN_FILE="${VIBESTACK_HOME:-$HOME/.vibestack}/projects/${SLUG:-unknown}/learnings.jsonl" if [ -f "$_LEARN_FILE" ]; then _LEARN_COUNT=$(wc -l < "$_LEARN_FILE" 2>/dev/null | tr -d ' ') echo "LEARNINGS: $_LEARN_COUNT entries loaded" if [ "$_LEARN_COUNT" -gt 5 ] 2>/dev/null; then ~/.vibestack/bin/vibe-learnings-search --limit 5 2>/dev/null || true fi else echo "LEARNINGS: none yet" fi ``` {{include lib/snippets/session-host.md}} {{include lib/snippets/decision-brief.md}} {{include lib/snippets/working-protocols.md}} {{include lib/snippets/state-protocols.md}} # Test-Driven Development ## Philosophy **Core principle**: Tests should verify behavior through public interfaces, not implementation details. Code can change entirely; tests shouldn't. **Good tests** are integration-style: they exercise real code paths through public APIs. They describe _what_ the system does, not _how_ it does it. A good test reads like a specification - "user can checkout with valid cart" tells you exactly what capability exists. These tests survive refactors because they don't care about inter...