Add test coverage that is_pair_active returns false for unregistered, zero-liquidity, and unset-liquidity pairs

[mikewheeleer]

Test the three falsey branches and the true branch of is_pair_active

Description

is_pair_active in src/lib.rs returns true only when a pair is both registered and has strictly positive reported liquidity. It short-circuits to false on an unregistered pair, and otherwise returns liquidity > 0, defaulting absent liquidity to 0. There is a subtlety here: a pair whose liquidity was never set by an oracle reads as 0 from this helper (not the i128::MAX sentinel that compute_route_fee uses), so is_pair_active is false for a freshly registered, never-funded pair even though compute_route_fee would treat it as unbounded. That divergence is worth pinning with tests so it is intentional and documented.

Requirements and context

• Repository scope: StableRoute-Org/Stableroute-contracts only.
• Test is_pair_active returns false for an unregistered pair.
• Test it returns false for a registered pair with liquidity explicitly set to 0 and for a registered pair with liquidity never set.
• Test it returns true for a registered pair with positive liquidity.
• Document (in the test doc comments and optionally a lib.rs note) the deliberate divergence between is_pair_active's 0-default and compute_route_fee's i128::MAX sentinel.

Suggested execution

• Fork the repo and create a branch
• git checkout -b test/contracts-is-pair-active-coverage
• Implement changes
  • Write code in: src/lib.rs — optional one-line doc clarification of the sentinel divergence; otherwise no production change.
  • Write comprehensive tests in: src/lib.rs (inline #[cfg(test)] mod test, near mod test_i18_read_surface) — cover all four branches.
  • Add documentation: note the divergence in docs/abi.md under is_pair_active.
  • Include NatSpec-style doc comments (///) on each new test, matching the existing style in lib.rs.
  • Validate security assumptions: read-only, no state change.
• Test and commit

Test and commit

• Run cargo fmt --all -- --check, cargo build, and cargo test.
• Cover edge cases: unregistered, zero liquidity, unset liquidity, and positive liquidity.
• Include the full cargo test output in the PR description.

Example commit message

test: cover is_pair_active across unregistered, zero, unset, and positive liquidity

Guidelines

• Minimum 95 percent test coverage for impacted modules.
• Clear, reviewer-focused documentation.
• Timeframe: 96 hours.

Community & contribution rewards

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[gloskull]

Hi, I’d love to work on this issue. I have 4 years of experience across backend, frontend, full-stack, and smart contract development. I understand the task clearly and can deliver a clean, efficient, well-tested solution on time, with strong focus on code quality and maintainability. My PR will be submitted in under 10 hours.