[CT-09] Write comprehensive unit tests for the escrow contract

[mftee]

Problem

The escrow contract in contracts/escrow/ handles all payment operations on the platform — fund holding, release, refund, and dispute resolution — but has minimal test coverage. Bugs in financial logic go undetected until real funds are lost.

Proposed Solution

Write a comprehensive test suite for the escrow contract inside contracts/package/tests/escrow/ using the Soroban SDK test harness with mock token contracts.

Note: All work must be done inside the contracts/package/ directory. Do not modify any existing contract files outside this folder.

Acceptance Criteria

• Tests cover fund_escrow: success path, double-funding the same escrow returns AlreadyFunded
• Tests cover release_funds: shipper can release, non-shipper caller returns Unauthorized
• Tests cover refund: only callable when shipment is cancelled, returns InvalidState otherwise
• Tests cover open_dispute: shipper and carrier can open, third party returns Unauthorized
• Tests cover admin_resolve: admin can release or refund, non-admin returns Unauthorized
• All tests use the Soroban Env::default() test environment and a mock SEP-41 token contract
• cargo test runs all tests successfully from contracts/package/tests/escrow/

[a-malik-gh]

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

I’d love to work on this task and contribute a solution for it.
I’ll review the requirements carefully and submit an implementation/update as soon as possible.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @a-malik-gh to this issue.

[drips-wave]

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

🧑‍💻 @a-malik-gh: 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.

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