// contracts/nativeModuleContract.ts
export type ContractResult<T> = {
  success: boolean;
  payload: T;
  error?: string;
};

export class NativeContractValidator {
  private registry: Map<string, (result: any) => boolean>;

  constructor() {
    this.registry = new Map();
  }

  register(moduleName: string, validator: (result: any) => boolean) {
    this.registry.set(moduleName, validator);
  }

  async validate(moduleName: string, nativeCall: () => Promise<any>): Promise<ContractResult<any>> {
    try {
      const result = await nativeCall();
      const validator = this.registry.get(moduleName);
      
      if (!validator) {
        return { success: false, payload: result, error: `No contract registered for ${moduleName}` };
      }

      const isValid = validator(result);
      return {
        success: isValid,
        payload: result,
        error: isValid ? undefined : `Contract violation for ${moduleName}: unexpected payload shape`
      };
    } catch (err) {
      return { success: false, payload: null, error: `Native call failed: ${(err as Error).message}` };
    }
  }
}

st Suite:**

// tests/nativeContracts/biometric.test.ts
import { NativeContractValidator } from '../../contracts/nativeModuleContract';
import { BiometricModule } from '../../native/BiometricModule';

const validator = new NativeContractValidator();

validator.register('BiometricModule', (result) => {
  return (
    typeof result === 'object' &&
    'available' in result &&
    'biometryType' in result &&
    ['FaceID', 'TouchID', 'Fingerprint', 'None'].includes(result.biometryType)
  );
});

test('validates biometric module contract on real device', async () => {
  const outcome = await validator.validate('BiometricModule', () => BiometricModule.isSensorAvailable());
  
  expect(outcome.success).toBe(true);
  expect(outcome.payload.biometryType).toBeDefined();
});

Rationale: Contracts decouple test logic from implementation details. They catch mock drift, platform-specific return types, and silent failures before they reach production. The validator pattern allows teams to version contracts alongside native module updates.

Phase 2: Adaptive Visual Assertions

Rigid testID or XPath selectors break when OEM skins shift layouts, change navigation insets, or apply system-level font scaling. Adaptive assertions use viewport-aware positioning and semantic matching rather than hardcoded element paths.

Implementation Strategy:

1. Replace static selectors with relative positioning and accessibility labels.
2. Use viewport boundary checks to verify elements remain within safe areas.
3. Implement visual regression guards that compare rendered frames against baseline snapshots, ignoring known OEM shift margins.

Code Example: Viewport-Aware Assertion Helper

// utils/viewportAssertions.ts
export type ViewportBounds = {
  x: number;
  y: number;
  width: number;
  height: number;
  safeAreaTop: number;
  safeAreaBottom: number;
};

export class ViewportAssertion {
  static isWithinSafeArea(bounds: ViewportBounds, element: { x: number; y: number; height: number }): boolean {
    const elementBottom = element.y + element.height;
    return (
      element.y >= bounds.safeAreaTop &&
      elementBottom <= bounds.safeAreaBottom &&
      element.x >= 0 &&
      element.x + element.width <= bounds.width
    );
  }

  static assertNotClipped(bounds: ViewportBounds, element: { x: number; y: number; width: number; height: number }) {
    const clipped = !this.isWithinSafeArea(bounds, element);
    if (clipped) {
      throw new Error(`Element clipped by OEM safe area: y=${element.y}, bottom=${element.y + element.height}, safeBottom=${bounds.safeAreaBottom}`);
    }
  }
}

Rationale: OEM fragmentation is inevitable. Instead of fighting it with device-specific overrides, assertions should validate that elements remain functional within the calculated safe area. This approach survives font scaling changes, gesture navigation bars, and notch/camera cutout variations.

Phase 3: Architecture-Aware Async Boundaries

The New Architecture eliminates JSON serialization but introduces synchronous JSI calls. Tests must explicitly document and handle sync vs async boundaries. Assuming all native calls are async leads to timing-dependent failures. Assuming all are sync breaks legacy Bridge compatibility.

Implementation Strategy:

1. Tag native module methods with @sync or @async metadata.
2. Generate test wrappers that automatically apply await or direct execution based on the tag.
3. Validate that sync calls do not block the JS thread beyond acceptable thresholds (typically <16ms for 60fps).

Rationale: Explicit boundary documentation prevents race conditions in tests and production. It also enables CI to flag performance regressions when sync calls exceed frame budgets.

Pitfall Guide

1. Mock Drift

Explanation: Static mocks are written once and rarely updated. Native modules receive platform updates, OEM patches, and library version bumps. Mocks diverge from reality, causing tests to pass while production fails. Fix: Replace static mocks with contract validators that run against actual native binaries. Version contracts alongside module releases.

2. Emulator-Only Validation

Explanation: Stock Android/iOS emulators lack manufacturer overlays, gesture navigation insets, and system-level accessibility settings. Tests pass in CI but fail on Samsung, Xiaomi, or Huawei devices. Fix: Integrate a cloud device farm or physical device lab into CI. Run a subset of integration tests on at least three OEM variants per release.

3. Rigid Selector Dependency

Explanation: testID and XPath selectors assume a fixed view hierarchy. OEM layout shifts, font scaling, and dynamic safe area calculations break these selectors. Fix: Use semantic locators (accessibility labels, role attributes) combined with viewport boundary assertions. Implement self-healing locators that fallback to visual proximity when exact matches fail.

4. Ignoring Failure States

Explanation: Tests only validate success paths. Real devices experience permission denials, hardware unavailability, network timeouts, and OEM popup interruptions. Fix: Explicitly test denial, timeout, and hardware-unavailable branches. Mock failure states in unit tests, but validate them against real native error codes in integration tests.

5. Async Timing Assumptions

Explanation: The legacy Bridge required async handling. JSI enables synchronous calls. Mixing assumptions causes race conditions, stale state reads, and flaky assertions. Fix: Document sync/async boundaries per module. Use explicit await patterns for async calls and direct execution for sync calls. Add frame-budget checks for sync operations.

6. CI Hardware Mismatch

Explanation: CI runs on lightweight emulators with limited GPU and CPU. Production runs on varied hardware. Performance tests and animation validations in CI do not reflect real-world behavior. Fix: Match CI specs to production baselines. Use hardware-accelerated emulators or physical devices for performance-sensitive suites. Profile GPU utilization and frame drops explicitly.

7. Over-Mocking the Bridge/JSI

Explanation: Teams mock the entire react-native namespace, hiding platform-specific behavior, TurboModule lazy-loading, and Fabric rendering cycles. Fix: Mock only pure JavaScript utilities. Allow native modules to load in integration tests. Use contract validators to assert behavior without replacing the native layer entirely.

Production Bundle

Action Checklist

• Audit native module mocks: Replace static mocks with contract validators that run on real devices.
• Implement viewport assertions: Validate element positioning against safe area bounds instead of hardcoded coordinates.
• Document sync/async boundaries: Tag native methods and generate test wrappers that respect JSI vs Bridge behavior.
• Add failure path coverage: Test permission denials, hardware unavailability, and OEM popup interruptions explicitly.
• Integrate OEM device matrix: Run integration suites on at least three manufacturer variants per release cycle.
• Profile frame budgets: Measure sync call duration and animation performance against 60fps thresholds.
• Version contracts alongside modules: Treat native module contracts as API contracts; break tests on schema changes.

Decision Matrix

Scenario	Recommended Approach	Why	Cost Impact
Early-stage prototype	Unit/Component tests only	Fast iteration, low overhead, validates core logic	Low
Production app with native modules	Contract testing + real-device E2E	Catches platform-specific failures before release	Medium
High-traffic fintech/health app	Full OEM matrix + visual regression + contract validation	Zero-tolerance for payment/permission failures	High
Legacy Bridge codebase	Async boundary documentation + emulator E2E	Mitigates timing issues without full architecture migration	Medium
New Architecture (JSI/Fabric)	Sync/async tagging + frame budget profiling	Leverages synchronous capabilities while preventing thread blocking	Medium-High

Configuration Template

# .codcompass/testing-config.yaml
version: 2.0

contracts:
  enabled: true
  registry_path: "./contracts/nativeModuleContract.ts"
  failure_policy: "block_release"

viewport_assertions:
  enabled: true
  safe_area_tolerance_px: 4
  font_scaling_threshold: 1.3

device_matrix:
  ci:
    - platform: "android"
      oem: "stock"
      api_level: 34
    - platform: "android"
      oem: "samsung"
      api_level: 33
    - platform: "ios"
      oem: "apple"
      version: "17.0"
  production_validation:
    - platform: "android"
      oem: "xiaomi"
      api_level: 34
    - platform: "android"
      oem: "huawei"
      api_level: 33

performance:
  sync_call_budget_ms: 16
  animation_frame_drop_threshold: 2
  gpu_profile_enabled: true

reporting:
  contract_violations: "fail_fast"
  viewport_clipping: "warn_and_log"
  flakiness_tracking: true

Quick Start Guide

1. Initialize Contract Registry: Create contracts/nativeModuleContract.ts and register validators for each native module your app uses. Define expected success shapes and error codes.
2. Add Viewport Assertions: Import ViewportAssertion into your E2E suite. Replace hardcoded coordinate checks with assertNotClipped calls that validate against dynamic safe area bounds.
3. Tag Async Boundaries: Add @sync or @async metadata to native module method definitions. Generate test wrappers that automatically apply await or direct execution based on the tag.
4. Configure Device Matrix: Update your CI pipeline to run contract tests on stock Android/iOS and at least two OEM variants. Enable viewport clipping warnings and contract violation blocking.
5. Execute Baseline Run: Trigger a full test suite. Review contract violations, viewport clipping logs, and frame budget reports. Fix native module mismatches and layout shifts before merging.