Assertion patterns

Assertion Patterns

Purpose

Transform T1-T4 violating assertions into real behavior verification. This skill provides pattern libraries for converting mock-based tests to tests that verify observable output.

When to Use

Load this skill when:

• Rewriting tests flagged by test-audit
• Generating verification scripts via bulwark-verify skill
• Implementing test-audit Step 7 rewrites

---

Prerequisite Checks (T0) - CRITICAL

Before checking T1-T4 violations, verify these prerequisites. Tests failing these checks are "testing nothing real" - they pass but provide zero confidence.

T0.1: Production Module Imports

Test files MUST import functions from actual production modules.

Valid	Invalid
import { calculate } from '../src/calculator'	Function defined within test file
from calculator import add	def add(a, b): return a + b in test

Detection:

• Scan test file for function definitions
• Check if tested functions are imported vs defined inline
• Flag if test calls functions not imported from production code

Violation Response:

"Test defines production logic inline. Move {function_name} to production module and import it. Tests should verify production code, not self-defined code."

T0.2: Separation of Concerns

Test files MUST NOT contain functions representing production logic.

Allowed in test files:

• Test functions (test_*, it(), describe())
• Test helpers/fixtures (make_*, create_*, setup_*)
• Mock factories (mock_*, fake_*, stub_*)
• Pytest fixtures (@pytest.fixture)

Not allowed:

• Business logic functions
• Utility functions that should be in production
• Any function that would make sense in src/

Detection:

• Identify all function definitions in test file
• Check naming patterns against allowed prefixes
• Flag functions that don't match test/helper patterns

T0.3: Function Naming Conventions

Functions in test files should follow specific naming patterns.

Legitimate Prefixes	Purpose
test_*	Test functions (pytest)
_* (underscore)	Private helpers
pytest_*	Pytest hooks
make_*, create_*	Factory helpers
mock_*, fake_*, stub_*	Mock factories
setup_*, teardown_*	Lifecycle helpers

Any other function definition raises suspicion - likely production code incorrectly placed in test files.

---

Pattern Categories

1. Function Call Verification

Anti-Pattern (Mock)	Real Pattern
expect(fn).toHaveBeenCalled()	const result = fn(); expect(result).toBe(expected)
expect(fn).toHaveBeenCalledWith(arg)	const result = fn(arg); expect(result.field).toBeDefined()
jest.spyOn(module, 'fn').mockReturnValue(x)	const result = module.fn(); expect(result).toBe(expected)

Transformation example:

// BEFORE (T1 violation - mocking system under test)
jest.spyOn(calculator, 'add').mockReturnValue(5);
expect(calculator.add(2, 3)).toBe(5);

// AFTER (real verification)
expect(calculator.add(2, 3)).toBe(5);  // Actually runs add()

2. Process Spawn Verification

Anti-Pattern (Mock)	Real Pattern
jest.spyOn(cp, 'spawn').mockReturnValue(mockProc)	const proc = spawn(...); await waitForReady(proc)
expect(spawn).toHaveBeenCalled()	expect(await isPortOpen(PORT)).toBe(true)
expect(spawn).toHaveBeenCalledWith(cmd, args)	const output = execSync(cmd); expect(output).toContain(expected)

Transformation example:

// BEFORE (T1 violation - mocking spawn)
const mockProcess = { on: jest.fn(), stdout: mockStream };
jest.spyOn(child_process, 'spawn').mockReturnValue(mockProcess);
await startProxy();
expect(child_process.spawn).toHaveBeenCalledWith('proxy', ['--port', '8080']);

// AFTER (real verification)
await startProxy();
expect(await checkPort(8080)).toBe(true);  // Port actually open
const response = await fetch('http://localhost:8080/health');
expect(response.status).toBe(200);  // Proxy actually responds

3. File Operation Verification

Anti-Pattern (Mock)	Real Pattern
jest.mock('fs')	Use real fs with temp directory
expect(fs.writeFile).toHaveBeenCalled()	expect(fs.existsSync(path)).toBe(true)
expect(fs.readFile).toHaveBeenCalledWith(path)	const content = fs.readFileSync(path); expect(content).toContain('expected')

Transformation example:

// BEFORE (T2 violation - call-only assertion)
await saveConfig(config);
expect(fs.writeFile).toHaveBeenCalled();

// AFTER (result verification)
await saveConfig(config);
expect(fs.existsSync(configPath)).toBe(true);
const saved = JSON.parse(fs.readFileSync(configPath, 'utf8'));
expect(saved.setting).toBe(config.setting);

4. HTTP Request Verification

Anti-Pattern (Mock)	Real Pattern
jest.mock('node-fetch')	Use MSW or test server
expect(fetch).toHaveBeenCalledWith(url)	const resp = await fetch(url); expect(resp.status).toBe(200)
Mock response data	Actual response from test server

Transformation example:

// BEFORE (T3 violation - mocking integration boundary)
jest.mock('node-fetch');
fetch.mockResolvedValue({ json: () => ({ id: 1 }) });
const user = await fetchUser(1);
expect(fetch).toHaveBeenCalledWith('/api/users/1');

// AFTER (real integration with MSW)
import { setupServer } from 'msw/node';
import { rest } from 'msw';

const server = setupServer(
  rest.get('/api/users/:id', (req, res, ctx) => {
    return res(ctx.json({ id: req.params.id, name: 'Test User' }));
  })
);

beforeAll(() => server.listen());
afterAll(() => server.close());

const user = await fetchUser(1);  // Real fetch, intercepted at network level
expect(user.name).toBe('Test User');

5. Database Verification

Anti-Pattern (Mock)	Real Pattern
expect(db.save).toHaveBeenCalled()	await db.save(data); const found = await db.find(id); expect(found).toBeDefined()
expect(db.delete).toHaveBeenCalledWith(id)	await db.delete(id); expect(await db.find(id)).toBeNull()
jest.mock('./database')	Use test database instance

Transformation example:

// BEFORE (T2 violation - call-only)
await saveUser(user);
expect(db.insert).toHaveBeenCalledWith('users', user);

// AFTER (result verification)
await saveUser(user);
const saved = await db.findOne('users', { id: user.id });
expect(saved).toBeDefined();
expect(saved.email).toBe(user.email);

---

T1-T4 Transformation Rules

T1: Mock System Under Test -> Remove mock, verify real output

The system under test should NEVER be mocked. Remove the mock and verify actual behavior.

// T1 violation: Mocking the function being tested
jest.spyOn(calculator, 'add').mockReturnValue(5);
expect(calculator.add(2, 3)).toBe(5);  // Always passes regardless of implementation

// Fixed: Test real implementation
expect(calculator.add(2, 3)).toBe(5);  // Fails if add() is broken

T2: Call-Only Assertion -> Add result assertion

Verifying a function was called is insufficient. Verify the RESULT of that call.

// T2 violation: Only checks call happened
await saveConfig(config);
expect(db.save).toHaveBeenCalled();  // Passes even if wrong data saved

// Fixed: Verify the actual saved data
await saveConfig(config);
const saved = await db.find(config.id);
expect(saved.value).toBe(config.value);  // Fails if wrong data saved

T3: Mock Integration Boundary -> Use test infrastructure

Integration tests should test real integration. Use MSW, test servers, or in-memory DBs.

// T3 violation: Mocking HTTP in integration test
jest.mock('node-fetch');
const data = await fetchUserData(id);  // Not testing real HTTP

// Fixed: Use MSW to intercept at network level
const server = setupServer(rest.get('/api/user/:id', handler));
const data = await fetchUserData(id);  // Real fetch, real HTTP, controlled response

T3+: Broken Integration Chain -> Chain real function outputs

Integration tests should chain real outputs through the pipeline.

// T3+ violation: Using mock data instead of real output
const mockOrder = { id: 1, items: [{ sku: 'ABC', qty: 2 }] };
await processOrder(mockOrder);  // Not testing real order creation

// Fixed: Chain real function outputs
const order = await createOrder({ sku: 'ABC', qty: 2 });  // Real order
await processOrder(order);  // Processes real order data
const result = await getOrderStatus(order.id);
expect(result.status).toBe('processed');

---

Quick Reference: Violation to Pattern

Violation	Pattern Category	Fix Strategy
T0.1	Prerequisites	Move function to production, import it
T0.2	Prerequisites	Extract non-test functions to src/
T0.3	Prerequisites	Rename or move functions
T1	Function Call	Remove mock, call real function
T2	Any category	Add result assertion after call
T3	HTTP/DB/Process	Use MSW, test DB, or spawn real process
T3+	Integration Chain	Chain real outputs, don't pass mocks

---

Diagnostic Output

Write diagnostic output to logs/diagnostics/assertion-patterns-{YYYYMMDD-HHMMSS}.yaml:

skill: assertion-patterns
timestamp: {ISO-8601}
diagnostics:
  t0_checks:
    t0_1_imports: pass|fail
    t0_2_separation: pass|fail
    t0_3_naming: pass|fail
  patterns_applied: [T1, T2, T3]
  transformations_suggested: 3
  files_analyzed: 1
  completion_status: success