test: Add error case coverage for critical paths

[claude]

Description

While the codebase has good test coverage (46 test files, 456+ validation tests), there are critical gaps in error case testing and edge case coverage for key user flows.

High-Priority Test Gaps

1. Onboarding Flow Error Cases

File: app/onboarding.tsx

Missing tests for:

• Supabase upsert failures (network errors, constraint violations)
• Profile refresh failures after form submission
• Race condition when profile update takes > 10 seconds (timeout handling)
• Apple Sign In metadata extraction edge cases

2. useDaysSober Hook Edge Cases

File: hooks/useDaysSober.ts

Missing tests for:

• Supabase query failures when fetching slip-ups
• DST (Daylight Saving Time) transition handling
• Midnight timer calculation edge cases
• Timezone change during app runtime

3. OAuth Token Extraction

File: contexts/AuthContext.tsx

Missing tests for:

• Malformed OAuth URLs
• Deep link URL processing with missing tokens
• Both hash and query params containing tokens (precedence)
• Concurrent OAuth flow race conditions

4. TaskCreationModal Error Scenarios

File: components/TaskCreationModal.tsx

Missing tests for:

• Template fetch failures
• Task insertion failures with specific error messages
• Invalid date range validation
• Empty sponsee list handling

5. Supabase Client Initialization

File: lib/supabase.ts

Missing tests for:

• Lazy initialization race conditions
• Storage adapter behavior verification
• Session persistence with malformed JSON

Mock Improvements Needed

Current Supabase mocks don't simulate:

• Row-level security (RLS) permission failures
• Constraint violations (unique email, foreign key)
• Rate limiting responses
• Connection timeout behaviors

Acceptance Criteria

• Add error case tests for onboarding flow
• Add timezone/DST edge case tests for useDaysSober
• Add OAuth error path tests for AuthContext
• Add error scenario tests for TaskCreationModal
• Improve Supabase mock to simulate failures
• Maintain 80% coverage threshold

Related

• Test coverage gap analysis from Daily Codebase Review 📋 Daily Codebase Review - 2025-12-10 #119

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[BillChirico]

Fixed in commit f6d8e36 - Added comprehensive error case coverage for critical paths including authentication, database operations, and API calls.