Add validation tests and coverage improvements for Send and feature flows

[Bluuefanatic]

Summary

This PR improves test coverage for critical wallet flows in Jam, with a focus on Send validation logic and feature flag evaluation.

It also introduces a minimal refactor to make validation logic testable without altering existing behavior.

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Key Changes

1. Validation Refactor (Minimal, Non-breaking)

• Extracted validation schema logic from:
  src/components/send/SendForm.tsx

• Into a dedicated module:
  src/components/send/sendValidationSchema.ts

• Behavior remains unchanged; logic is now reusable and testable in isolation.

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2. Added Validation Tests

Send Form Validation

SendForm.validation.test.ts

Covers:

• Address validation
  (valid, malformed, null/undefined, wrong network)
• Amount validation
  (positive, zero, negative, NaN, large values)
• Sweep mode behavior
• Collaborator constraints
  (boundaries and malformed inputs)

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Collaborative Send Validation

collaborativeSend.validation.test.ts

Covers:

• Request-level validation
• Invalid inputs
  (NaN, null, malformed values)
• Sweep behavior (amount_sats = 0)
• Collaborator constraints and edge cases

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3. Feature Flag Tests (Adapted to v2)

The file src/constants/features.ts referenced in the task is not present in the v2 branch.

Feature logic is currently implemented via:

• src/hooks/useFeatures.ts
• src/constants/debugFeatures.ts

Tests were added to validate:

• Enabled/disabled feature states
• Missing or undefined feature flags
• Developer/debug overrides

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4. Coverage Improvements

• Added comprehensive edge-case testing for validation logic
• Focused on safety-critical paths affecting transaction correctness

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Notes

• Referenced files (helpers.ts, features.ts) are not present in v2
• Testing approach was adapted to match the current architecture
• Validation logic was minimally extracted strictly for testability
• No behavioral changes were introduced

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Why This Matters

Jam handles real Bitcoin transactions, where validation errors can lead to:

• Incorrect transaction construction
• Invalid collaborator configurations
• Unintended fund behavior

Improving test coverage for these flows reduces regression risk and increases overall reliability.

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