Test driven development

Test-Driven Development

Relies on BDK foundation (STARTUP_INSTRUCTIONS.md) for project context and MCP tool preference.

Rigid, gated process. Follow every gate in order. No skipping.

digraph tdd {
    rankdir=TB
    node [shape=box, style="rounded,filled", fillcolor="#f0f0f0"]

    start [label="Receive test cases\n+ implementation spec", shape=ellipse, fillcolor="#d4edda"]
    g0 [label="GATE 0\nLoad project context\nFind test conventions", fillcolor="#cce5ff"]
    g1 [label="GATE 1\nWrite tests from ✅ bullets\nGap scan for edge cases", fillcolor="#cce5ff"]
    g2 [label="GATE 2\nDelegate to test-runner\nExpect: ALL FAIL", fillcolor="#cce5ff"]
    tests_pass [label="Tests\nPASS?", shape=diamond, fillcolor="#fff3cd"]
    stop_investigate [label="STOP\nImplementation exists\nor test is wrong.", shape=ellipse, fillcolor="#f8d7da"]
    g3 [label="GATE 3\nImplement as described in plan", fillcolor="#cce5ff"]
    g4 [label="GATE 4\nDelegate to test-runner\nExpect: ALL PASS", fillcolor="#cce5ff"]
    green_pass [label="Tests\nPASS?", shape=diamond, fillcolor="#fff3cd"]
    fix_attempt [label="Fix implementation\n(attempt N/3)", fillcolor="#fff3cd"]
    too_many [label="STOP\nAsk user", shape=ellipse, fillcolor="#f8d7da"]
    attempts_left [label="Attempts\n< 3?", shape=diamond, fillcolor="#fff3cd"]
    done [label="Task done ✓", shape=ellipse, fillcolor="#d4edda"]

    start -> g0
    g0 -> g1
    g1 -> g2
    g2 -> tests_pass
    tests_pass -> stop_investigate [label="YES (unexpected)"]
    tests_pass -> g3 [label="NO (expected)"]
    g3 -> g4
    g4 -> green_pass
    green_pass -> done [label="YES"]
    green_pass -> attempts_left [label="NO"]
    attempts_left -> fix_attempt [label="YES"]
    attempts_left -> too_many [label="NO"]
    fix_attempt -> g4
}

---

Input

Plan task provides:

**Test cases:**
- ✅ Positive: given [input], expects [output]
- ❌ Negative: given [invalid input], raises [error]

**Implementation:** [what to build — file path, class, method]

---

GATE 0: Load Context

Read project context:

• Test file conventions (location, naming)
• Test framework
• Existing patterns (fixtures, factories, assertions)

Tool-assisted discovery:

!python3 ${CLAUDE_PLUGIN_ROOT}/scripts/inject.py --chain ${CLAUDE_PLUGIN_ROOT}/fragments/tool-tiers/search.chain.json

Using the search tools above: find existing tests to avoid duplication, understand blast radius to prioritize edge cases.

Identify test file path per project conventions.

Cannot proceed without understanding project test conventions.

---

GATE 1: Write Tests

Write test per ✅ bullet. Follow conventions from GATE 0.

Before writing, scan spec for:

• Boundary conditions (empty list, zero, first/last element)
• Invalid types or missing required fields
• Unexpected None or absent optional data

Add tests for meaningful gaps. No padding.

Negative tests (❌ bullets): Write when real value exists. Skip if no meaningful failure modes.

Cannot proceed until every ✅ bullet has corresponding test.

---

GATE 2: Verify RED

Inject test command: !python3 ${CLAUDE_PLUGIN_ROOT}/scripts/get_settings.py test-tools

Delegate to /bdk:test-runner agent using injected command above (fall back to detecting from project context if unavailable):

Run the project's test suite against: {test_file_path}
Expected: ALL written tests FAIL

Tests PASS: Stop. Implementation already exists or test wrong.

Tests FAIL as expected: Proceed to GATE 3. ✓

---

GATE 3: Implement

Implement per plan task. Focused on passing tests — no extra features.

---

GATE 4: Verify GREEN

Delegate to /bdk:test-runner agent using injected command from GATE 2:

Run the project's test suite against: {test_file_path}
Expected: ALL tests PASS

Tests FAIL: Fix implementation. Max 3 attempts. After 3, stop and ask user.

Tests PASS: Proceed. ✓

---

Anti-Patterns

• ❌ Skipping GATE 2 ("I know it will fail")
• ❌ Writing implementation before tests exist
• ❌ Forcing negative test when no real failure mode exists
• ❌ Hardcoding test commands — always detect project's test runner