test(contracts): implement boundary testing for arithmetic operations…

[Stanley-Owoh]

Title:
test(contracts): implement boundary testing for arithmetic operations in contracts

Body:

Summary

• Implement comprehensive boundary testing for arithmetic operations in smart contracts
• Add tests for checked_add, checked_sub, checked_mul, and checked_div operations
• Achieve >90% test coverage target with edge cases and integration tests
• Follow OWASP security guidelines for integer overflow prevention

Implementation Details

• New Module: contracts/token-factory/src/arithmetic_boundary_tests.rs
  • checked_add_boundary_tests: i128::MAX/MIN boundaries, token supply overflow
  • checked_sub_boundary_tests: Underflow protection, burn/claim calculations
  • checked_mul_boundary_tests: Vesting/staking reward overflow scenarios
  • checked_div_boundary_tests: Division by zero, boundary divisions
  • integration_boundary_tests: Max supply, fee calculation boundaries
  • comprehensive_edge_case_tests: Zero values, full i128 operation suites
  • security_boundary_tests: OWASP compliance, state consistency

Testing Evidence

• Tests cover boundary values: i128::MAX, i128::MIN, 0
• Includes property-based edge cases for arithmetic operations
• Integration tests verify state consistency after boundary operations
• All tests follow existing project patterns from mutation_arithmetic_tests.rs

Security

• Prevents integer overflow/underflow using Rust's checked_* operations
• Follows OWASP Secure Coding Practices for numeric types
• Validates all arithmetic operations maintain security invariants

Files Changed

• contracts/token-factory/src/arithmetic_boundary_tests.rs (new file)
• contracts/token-factory/src/lib.rs (module declaration added)

Closes #810

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