Add Comprehensive Automation Tests for Single Family Refresh Token (SFRT) Flows

[Copilot]

This PR adds comprehensive automation tests for Single Family Refresh Token (SFRT) functionality to ensure robust testing coverage for all SFRT scenarios and edge cases. The current codebase has SFRT implementation but lacks comprehensive test coverage for all the flows and edge cases.

Overview

Single Family Refresh Tokens (SFRTs) are a critical feature that enables seamless Single Sign-On (SSO) across multiple applications within an app family. This test suite provides complete automation coverage to validate SFRT functionality across all supported scenarios.

Test Files Added

Core Functionality Tests

• MSIDFamilyRefreshTokenTests.m - Tests core MSIDFamilyRefreshToken class functionality including initialization, properties, credential type validation, and cache item generation
• MSIDFRTEnabledStatusTests.m - Tests all FRT enablement status scenarios including feature flag controls, client-side disabling, and error conditions

Token Management Tests

• MSIDDefaultTokenCacheAccessorSFRTTests.m - Tests SFRT token retrieval logic, fallback mechanisms, and integration with the token cache
• MSIDSFRTStorageTests.m - Tests SFRT storage logic based on feature flag status and family ID presence

Request Flow Tests

• MSIDSilentTokenRequestSFRTTests.m - Tests token acquisition flows with SFRT, including app refresh token fallback to family refresh token scenarios
• MSIDInteractiveTokenRequestSFRTTests.m - Tests FRT support in interactive flows including custom header injection

Error Handling and Integration Tests

• MSIDSFRTErrorHandlingTests.m - Tests client mismatch scenarios and error recovery mechanisms
• MSIDSFRTIntegrationTests.m - End-to-end SFRT flow tests covering multi-app family scenarios

Key Test Coverage Areas

Feature Management

• Feature flag enablement/disablement scenarios
• Client-side FRT disabling functionality
• Keychain item validation and cache corruption recovery
• Combined feature flag and client setting scenarios

Token Retrieval and Storage

• SFRT retrieval when enabled vs disabled
• Fallback to regular refresh tokens when SFRT unavailable
• Cross-accessor token lookup functionality
• Family ID-based storage decision logic
• Multi-accessor storage coordination

Request Flows

• App refresh token failure → FRT fallback scenarios
• FRT failure → client mismatch error handling
• Token type selection logic and completion handler execution
• Custom header injection for FRT support in interactive flows
• Force refresh scenarios and mixed family token handling

Error Scenarios

• Client mismatch error handling and family ID cache updates
• Server error processing and invalid token removal
• Cache corruption recovery mechanisms
• Network error handling with exponential backoff
• Multi-threaded error scenarios

Integration Scenarios

• Multi-app family token sharing and cross-app SSO validation
• Complete SSO lifecycle from initial authentication through token refresh
• Multi-family scenarios with proper token isolation
• End-to-end flow verification with error recovery

Implementation Quality

• Follows Existing Patterns: Uses established XCTest framework patterns consistent with existing tests
• Comprehensive Mocking: Leverages MSIDTestSwizzle, MSIDTestURLSession, and MSIDTestURLResponse for reliable test isolation
• Reusable Helpers: Includes comprehensive helper methods for common test setup and validation scenarios
• Edge Case Coverage: Tests all identified edge cases, error conditions, and boundary scenarios
• Integration Ready: Uses existing test infrastructure (MSIDTestCacheAccessorHelper, MSIDTestIdentifiers, etc.)

Benefits

1. Comprehensive Coverage: Tests all SFRT code paths and edge cases identified in the requirements
2. Regression Prevention: Catches issues early in the development cycle through automated validation
3. Living Documentation: Tests serve as executable documentation of expected SFRT behavior
4. Safe Refactoring: Enables confident code changes with comprehensive test coverage
5. Quality Assurance: Ensures SFRT functionality works correctly across all supported scenarios

The test suite provides complete automation coverage for SFRT functionality, ensuring robust validation of all flows, edge cases, and multi-app integration scenarios as specified in the original requirements.

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