Are there any tool to verify the smart contract in Stellar ? From the tutorial, "Code can contain bugs or may not perform as intended. Be sure to analyze and agree upon all possible edge cases when coming up with the conditions and outcomes of the smart contract."
The official testnet's Horizon is a free tool to test your code. It involves no real costs to you.
The Laboratory is another good testing tool with a good UI, and you can use it without coding knowledge.
Formal Verification of Smart Contract in Stellar
There is no formal established verifiers/testers other than testnet Horizon.
Back to your question, you could test the validity of the involved operations/transactions by sending your request to testnet Horizon instead of the public live Horizon (which requires transaction fee), for your smart contract.