Basic tests (unit & integration) for core flows

[RafaelJohn9]

Create unit tests for backend helpers and integration tests for the simulated token flow (tokenize -> transfer -> verify).

Description (deep):
Tests increase reliability. Unit-test the canonical JSON generator, hash function, and IPFS upload mock. Integration tests should run against Hedera testnet (or a mocked Hedera SDK) to assert token creation and transfers succeed and DB is updated accordingly. For hackathon scope, focus on deterministic unit tests and a small end-to-end integration test demonstrating token creation and a single transfer.

Acceptance checklist

• Add unit tests for metadata generation and hashing
• Add unit tests for IPFS upload (use mocked client)
• Add an integration test that mints a token and transfers a small quantity to a dummy buyer (testnet or mocked)
• Integrate tests into npm test or similar command

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