Testing agents with subagents

Testing Agents With Subagents

Overview

This skill applies TDD methodology to agent development — RED (observe failures), GREEN (fix agent definition), REFACTOR (edge cases and robustness) — with subagent dispatch as the execution mechanism.

Test what the agent DOES, not what the prompt SAYS. Evidence-based verification only: capture exact outputs from subagent dispatch, verify every prompt change through testing. Always test via the Task tool, always test via the Task tool rather than reading prompts.

Minimum test counts vary by agent type: Reviewer agents need 6 cases (2 real issues, 2 clean, 1 edge, 1 ambiguous), Implementation agents 5 cases (2 typical, 1 complex, 1 minimal, 1 error), Analysis agents 4 cases (2 standard, 1 edge, 1 malformed), Routing/orchestration 4 cases (2 correct route, 1 ambiguous, 1 invalid). No agent is simple enough to skip testing — get human confirmation before exempting any agent.

Each test runs in a fresh subagent to avoid context pollution. After any fix, re-run ALL test cases to catch regressions. One fix at a time — you cannot determine what changed the outcome with multiple simultaneous fixes.

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Reference Loading Table

Signal	Load These Files	Why
example-driven tasks, errors	examples-and-errors.md	Loads detailed guidance from examples-and-errors.md.
dispatch-and-capture, negative, consistency, A/B, and routing-verification test patterns	testing-patterns.md	Loads detailed guidance from testing-patterns.md.

Instructions

Phase 0: PREPARE — Understand the Agent

Goal: Read the agent definition and understand what it claims to do before writing tests.

Step 1: Read the agent file

# Read agent definition
cat agents/{agent-name}.md

# Read any referenced skills
cat skills/{skill-name}/SKILL.md

Step 2: Identify testable claims

Extract concrete, testable behaviors from the agent definition:

• What inputs does it accept?
• What output structure does it produce?
• What routing triggers should activate it?
• What error conditions does it handle?
• What skills does it invoke?

Step 3: Determine minimum test count

Agent Type	Minimum Tests	Required Coverage
Reviewer agents	6	2 real issues, 2 clean, 1 edge, 1 ambiguous
Implementation agents	5	2 typical, 1 complex, 1 minimal, 1 error
Analysis agents	4	2 standard, 1 edge, 1 malformed
Routing/orchestration	4	2 correct route, 1 ambiguous, 1 invalid

No gate — this phase is preparation. Move directly to Phase 1.

Phase 1: RED — Observe Current Behavior

Goal: Run agent with test inputs and document exact current behavior before any changes.

Step 1: Define test plan

Write the test plan to a file before executing — this creates a reproducible baseline. See ${CLAUDE_SKILL_DIR}/references/examples-and-errors.md for the Test Plan template.

Step 2: Dispatch subagent with test inputs

Use the Task tool to dispatch the agent (see dispatch template in references/examples-and-errors.md). Each test runs in a fresh subagent — this prevents context pollution from earlier tests affecting later ones.

Step 3: Capture results verbatim

Document exact agent outputs. See the verbatim result capture template in references/examples-and-errors.md.

Step 4: Identify failure patterns

• Which test categories fail (happy path, error, edge)?
• Are failures structural (missing sections) or behavioral (wrong answers)?
• Do failures correlate with input characteristics?

Gate: All test cases executed. Exact outputs captured verbatim. Failures documented with specific issues identified. Proceed only when gate passes.

Phase 2: GREEN — Fix Agent Definition

Goal: Update agent definition until all test cases pass. One fix at a time.

Step 1: Prioritize failures

Triage failures by severity — see the Failure Severity table in ${CLAUDE_SKILL_DIR}/references/examples-and-errors.md (Critical/High/Medium/Low).

Step 2: Diagnose root cause

Map the failure type to a fix approach — see the Root Cause → Fix Approach table in references/examples-and-errors.md.

Step 3: Make one fix at a time

Change one thing in the agent definition. Re-run ALL test cases. Document which tests now pass/fail.

Make one fix at a time — you cannot determine which change was effective. Same debugging principle: one variable at a time.

Step 4: Iterate until green

Repeat Step 3 until all test cases pass. If a fix causes a previously passing test to fail, revert and try a different approach. Track fix iterations using the Fix Log template in references/examples-and-errors.md.

Gate: All test cases pass. No regressions from previously passing tests. Can explain what each fix changed and why. Proceed only when gate passes.

Phase 3: REFACTOR — Edge Cases and Robustness

Goal: Verify agent handles boundary conditions and produces consistent outputs.

Step 1: Add edge case tests

See the Edge Case Categories table in ${CLAUDE_SKILL_DIR}/references/examples-and-errors.md (Empty / Large / Unusual / Ambiguous inputs).

Step 2: Run consistency tests

Run the same input 3 times. Outputs should be consistent:

• Same structure
• Same key findings (for analysis agents)
• Acceptable variation in phrasing only

If inconsistent: add more explicit instructions to the agent definition. Re-test.

Step 3: Run regression suite

Re-run ALL test cases (original + edge cases) to confirm nothing broke during refactoring.

Step 4: Document final test report

See the Test Report template in ${CLAUDE_SKILL_DIR}/references/examples-and-errors.md.

Gate: Edge cases handled. Consistency verified. Full suite green. Test report documented. Fix is complete.

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Error Handling

See ${CLAUDE_SKILL_DIR}/references/examples-and-errors.md for error cases: agent-type-not-found, inconsistent-outputs, subagent-timeout, agent-asks-questions.

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Examples

See ${CLAUDE_SKILL_DIR}/references/examples-and-errors.md for worked examples: testing a new reviewer agent, testing after agent modification, testing routing logic.

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References

Integration

• agent-comparison: A/B test agent variants
• agent-evaluation: Structural quality checks
• test-driven-development: TDD principles applied to agents

Reference Files

• ${CLAUDE_SKILL_DIR}/references/testing-patterns.md: Dispatch patterns, test scenarios, eval harness integration
• ${CLAUDE_SKILL_DIR}/references/examples-and-errors.md: Worked examples (new reviewer, modification, routing) and error handling (agent-not-found, inconsistency, timeout, question-asking)