[P1] Expand contract tests beyond snapshot-style subscription registry cases

[Calebux]

Summary

The current Rust test footprint appears narrow relative to the stated contract surface.

Scope

• Area: blockchain
• Priority: P1
• Backlog ID: #74

Acceptance Criteria

• Each contract has positive and negative test coverage.
• Invariant tests cover authorization, duplicate prevention, and cancellation rules.
• CI publishes contract test results clearly.

Implementation Notes

• Keep the implementation aligned with current architecture decisions and security constraints in this repo.
• Include tests for changed behavior and update docs where relevant.

Definition of Done

• Acceptance criteria met
• Tests added/updated and passing
• Documentation updated
• No security regressions introduced

Links

• Backlog source: docs/repo-issue-backlog-2026-05.md

[Shoboyan1]

@Shoboyan1 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I’d like to work on this issue because improving contract test coverage is essential for ensuring reliability, security, and maintainability in blockchain systems, especially within a growing ecosystem like Stellar Wave. Expanding the tests beyond snapshot-style cases is a valuable opportunity to strengthen the contract surface and contribute meaningful quality improvements. I have a Computer Science background with experience in Rust fundamentals, software testing concepts, Git/GitHub workflows, and collaborative development, and I’m eager to apply and deepen these skills while contributing to blockchain-focused open-source infrastructure.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Shoboyan1 to this issue.

[drips-wave]

Congratulations, @Shoboyan1! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @Shoboyan1: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊