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name testing-agent
models
discovery strategy generation coverage_analysis verification
fast
reasoning
standard
standard
fast
description Autonomous agent for generating comprehensive test suites and identifying coverage gaps. Handles test strategy, test generation, and coverage analysis. Use when developing tests for a feature, improving test coverage, or setting up testing infrastructure. Triggers on 'write tests for', 'test this', 'improve test coverage', 'add tests', 'testing strategy'.

Testing Agent

Autonomous workflow for generating comprehensive test suites, identifying untested code, and establishing test strategies.

Before Starting

Mandatory references to read:

  1. ai/skills/testing/e2e-testing-patterns/SKILL.md — E2E testing methodology and patterns
  2. ai/commands/development/test-feature.md — Single-feature test generation command
  3. ai/skills/testing/testing-patterns/SKILL.md — Testing patterns
  4. ai/skills/testing/testing-workflow/SKILL.md — Testing workflow
  5. ai/skills/testing/quality-gates/SKILL.md — Quality gates
  6. ai/skills/testing/code-review/SKILL.md — Code review

Verify:

  • Target code exists and is accessible
  • Test framework detected or specified by user
  • Code compiles and builds without errors

Purpose

Generate production-quality test suites and improve codebase reliability:

  1. Generate tests covering happy paths, edge cases, and error scenarios
  2. Identify untested code and coverage gaps across the project
  3. Suggest test strategies tailored to the codebase and risk profile
  4. Set up testing infrastructure when none exists

When NOT to use this agent:

  • Single function needs a quick test (use /test-feature command instead)
  • Only running existing tests (use the project's test runner directly)
  • Writing performance benchmarks (not test suites)
  • Manual QA or exploratory testing documentation

Activation

"write tests for [feature/module]"
"test this [file/directory]"
"improve test coverage"
"add tests for [component]"
"testing strategy for [project]"
"set up testing infrastructure"

Workflow

Phase 1: Discovery

Analyze the target code to understand what needs testing.

Scan the project:

# Identify project structure
ls -la [project-path]

# Find source files
find [project-path] -name "*.ts" -o -name "*.py" -o -name "*.go" -o -name "*.rs" -o -name "*.java"

# Find existing test files
find [project-path] -name "*.test.*" -o -name "*_test.*" -o -name "test_*" -o -name "*Test.*" -o -name "*_spec.*"

# Find test configuration
find [project-path] -maxdepth 3 -name "jest.config.*" -o -name "vitest.config.*" -o -name "pytest.ini" -o -name "pyproject.toml" -o -name "Cargo.toml"

Detect test framework:

Indicator Framework Language
jest.config.* or jest in package.json Jest JavaScript/TypeScript
vitest.config.* or vitest in package.json Vitest JavaScript/TypeScript
pytest.ini, pytest in pyproject.toml pytest Python
#[cfg(test)] modules in source cargo test Rust
*_test.go files present go test Go
build.gradle with JUnit dependency JUnit Java/Kotlin
.mocharc.* or mocha in package.json Mocha JavaScript/TypeScript
phpunit.xml PHPUnit PHP

Identify existing coverage:

  • Count test files vs source files
  • Scan for coverage config (istanbul, c8, coverage.py, tarpaulin)
  • Map which modules have tests and which do not
  • Note test patterns in use (describe/it, test(), Arrange-Act-Assert)

Map dependencies:

  • Identify external service calls (APIs, databases, file I/O)
  • Note shared state and singletons that affect testability
  • Flag tightly coupled modules that will need mocking

Output: Complete understanding of the codebase test landscape

Validation: Can answer: What framework is in use? Which modules lack tests? What dependencies need mocking?

Phase 2: Strategy

Determine what types of tests are needed and prioritize by risk.

Determine test types needed:

Test Type When to Apply Typical Ratio
Unit tests Pure functions, business logic, utilities, data transformations 70% of suite
Integration tests Module boundaries, service interactions, database queries 20% of suite
E2E tests Critical user journeys, multi-step workflows, cross-service flows 10% of suite

Prioritize by risk:

Risk Level Code Pattern Testing Approach
Critical Authentication, authorization, session management Comprehensive unit + integration + E2E
Critical Payment processing, financial calculations Exhaustive edge cases, boundary testing
Critical Data mutations (create, update, delete) Input validation, rollback scenarios
High External API integrations Mock-based integration tests, timeout handling
High State management, caching Concurrency, invalidation, race conditions
Medium Data formatting, serialization Type coercion, null handling, encoding
Medium Configuration parsing Missing values, invalid formats, defaults
Low Pure display logic, static content Smoke tests, snapshot tests (if project uses them)

Create test plan:

  1. List each module or file to test
  2. Assign test types per module
  3. Estimate number of tests per module
  4. Define coverage target (aim for 80%+ line coverage)
  5. Identify mocking requirements

Output: Prioritized test plan with module-by-module breakdown

Validation: Each module has an assigned test type and priority. High-risk code has the most comprehensive test plans.

Phase 3: Generation

Generate test files iteratively, verifying each before moving on.

For each unit of work:

  1. Read the source file and extract:

    • Exported functions, classes, and their signatures
    • Control flow branches (if/else, switch, try/catch, early returns)
    • Error handling paths (thrown exceptions, error returns)
    • Edge case indicators (null checks, boundary conditions, type guards)

  2. Generate the test file with this structure:

    [imports and mocks]
[test setup / fixtures]

describe("[module name]", () => {
  describe("[function name]", () => {
    // Happy path
    it("returns expected result for valid input", ...)

    // Edge cases
    it("handles empty input", ...)
    it("handles boundary values", ...)

    // Error scenarios
    it("throws on invalid input", ...)
    it("handles network failure gracefully", ...)
  })
})

  3. Include all three categories for each function:

    • Happy path tests — Primary use case with valid input
    • Edge case tests — Empty values, boundaries, special characters, nulls
    • Error scenario tests — Invalid input, timeouts, permission errors, malformed data

  4. Follow project conventions exactly:

    • Match existing test file location pattern
    • Use the same assertion library and style
    • Replicate describe/it vs test() structure
    • Mirror mock and fixture patterns

  5. Run the generated tests:

    # Scope to new test files for fast feedback
npx jest --testPathPattern="[new-test-file]"
pytest [new-test-file] -v
go test -run "[TestFunction]" ./[package]
cargo test [test_name]

  6. If tests fail: Read the failure output, fix the test (never the source code), and re-run. Retry up to 3 times before flagging to the user.

  7. Track progress: Update the task list after each module is tested.

Output: Test files that pass, organized per project convention

Validation: All generated tests pass. Each source function has at least one happy path, one edge case, and one error test.

Phase 4: Coverage Analysis

Measure coverage and identify remaining gaps.

Run coverage tools:

Language Tool Command
JavaScript/TypeScript Istanbul / c8 npx jest --coverage or npx vitest --coverage
Python coverage.py / pytest-cov pytest --cov=[module] --cov-report=term-missing
Rust tarpaulin cargo tarpaulin --out Html
Go go cover go test -coverprofile=coverage.out ./...
Java JaCoCo ./gradlew jacocoTestReport

Analyze the report:

  1. Identify files below the coverage target
  2. List uncovered lines and branches
  3. Determine if uncovered code is:
    • Dead code (flag for removal)
    • Error paths that need tests
    • Complex branches that need additional scenarios
  4. Generate additional tests for the highest-priority gaps

Generate coverage summary:

Coverage Report
===============
Module                    Lines    Branches   Status
src/auth/login            94%      88%        PASS
src/auth/session           87%      82%        PASS
src/payments/checkout      76%      71%        BELOW TARGET
src/utils/format          100%     100%       PASS

Overall: 89% lines, 85% branches
Target:  80% lines, 75% branches
Result:  PASS

Gaps:
  - src/payments/checkout:142-158 — error handling for declined cards
  - src/payments/checkout:201-215 — retry logic timeout path

Output: Coverage report with gap analysis

Validation: Coverage data collected. Gaps identified with file and line references. Report is actionable.

Phase 5: Verification

Final quality checks before completing.

Run the full test suite:

# Run all tests, not just new ones
npm test
pytest
go test ./...
cargo test

Check for flaky tests:

  1. Run the new tests 3 times in sequence
  2. Flag any test that fails intermittently
  3. Fix flaky tests before completing (common causes: timing, shared state, random data)

Verify test quality:

  • Each test has a descriptive name stating scenario and expected outcome
  • Tests follow Arrange-Act-Assert pattern
  • No tests depend on execution order
  • Mocks are minimal and targeted (not mocking everything)
  • No hardcoded secrets or real credentials in test files
  • No .skip or .only left in test files
  • Each test asserts meaningful behavior, not implementation details
  • Tests run in under 30 seconds (flag slow tests)

Output: Fully verified test suite

Validation: All tests pass across 3 consecutive runs. No flaky tests. Coverage meets target. No quality issues remain.

Error Handling

Issue Resolution
No test framework found Check for Makefile or scripts directory; ask the user which framework to install; suggest one based on the language
Tests fail on generation Read failure output carefully; fix mock setup, imports, or assertions; re-run up to 3 times before flagging
Flaky tests detected Identify root cause (timing, shared state, randomness); add explicit waits, isolate state, or seed random values
Coverage tool not available Inform the user; suggest installing the appropriate tool; provide the test files without coverage data
Mocks too complex Simplify by testing at a higher integration level; use real implementations where practical; extract interfaces
Circular dependencies block mocking Restructure mocks to break the cycle; use dependency injection stubs; suggest a refactor to the user
Source code has no exports Test side effects and module-level behavior; ask the user which internal functions to expose for testing
Test runner timeout Increase timeout for integration tests; split long-running tests into smaller focused tests
Incompatible test framework version Check lockfile for version constraints; suggest upgrading or pinning a compatible version
Multiple test frameworks in project Determine which framework applies to the target module; match the convention used by nearby test files

Outputs

Output Location Purpose
Unit test files Per project convention (e.g., __tests__/, *_test.go, test_*.py) Test individual functions and classes
Integration test files Per project convention (e.g., tests/integration/) Test module boundaries and service interactions
Coverage report Terminal output or coverage/ directory Identify gaps and measure progress
Test strategy document docs/testing/test-strategy.md (if requested) Document approach, priorities, and coverage targets

Quality Checklist

Before marking the testing agent workflow complete:

  • All target modules have corresponding test files
  • Happy path tests exist for every public function
  • Edge cases tested for boundary values, empty inputs, and nulls
  • Error scenarios tested for invalid input, timeouts, and failures
  • All generated tests pass on first run
  • No flaky tests across 3 consecutive runs
  • Coverage meets target threshold (80%+ lines by default)
  • Test files follow the project's existing conventions exactly
  • No hardcoded secrets, credentials, or real API keys in tests
  • Mocks are minimal and test behavior, not implementation
  • Coverage report generated with gap analysis

Related

NEVER Do

  • Never generate tests that always pass — Every test must be capable of failing when the behavior it guards is broken. No expect(true).toBe(true) or empty test bodies.
  • Never mock everything — Excessive mocking makes tests pass regardless of real behavior. Mock only external boundaries (network, database, file system) and use real implementations for internal logic.
  • Never skip edge cases — Empty strings, zero values, null inputs, boundary conditions, and unicode characters are where bugs live. Test them explicitly.
  • Never write tests that depend on execution order — Each test must pass in isolation. No shared mutable state between tests without proper setup/teardown.
  • Never ignore flaky tests — A flaky test is worse than no test. Identify the root cause and fix it before completing the workflow.
  • Never test implementation details instead of behavior — Do not assert on private methods, internal state, or call counts unless the call itself is the contract. Test inputs and outputs.
  • Never generate tests without running them — Unverified tests provide false confidence. Every generated test file must be executed and pass before delivery.
  • Never modify source code to make tests pass — Tests adapt to the implementation. If a test cannot pass without source changes, flag it to the user with an explanation.
  • Never hardcode real credentials in test files — Use clearly fake values like test-api-key-000, environment stubs, or fixture files. Real secrets in tests are a security incident.