_You can follow along with the video course from here._ ### Introduction In this lesson, we'll delve into _end-to-end testing_ of a Solidity contract's deployment and execution. ### Deployment Transaction First, we need to _compile_ the contract to ensure the code is correct. On Remix, set the **injected provider** to MetaMask and confirm it is properly synced to the testnet. Ensure you have some Sepolia Ether (ETH) in your wallet if you plan to deploy the contract on Sepolia.  We'll deploy the `FundMe` contract by clicking deploy and then confirming the transaction in MetaMask, which may take some time. ### Contract Interaction After successfully deploying the `FundMe` contract, you'll see several buttons to interact with it: - **Red button**: Payable functions (e.g., `fund`) - **Orange button**: Non-payable functions (e.g., `withdraw`) - **Blue buttons**: `view` and `pure` functions The `fund` function allows us to send ETH to the contract (minimum 5 USD). The `owner` of the contract is our MetaMask account, as the **constructor** sets the deployer as the owner. > 🗒️ **NOTE**:br > If the `fund` function is called without any value or with less than 5 USD, you will encounter a gas estimation error, indicating insufficient ETH, and gas will be wasted. ### Successful Transaction If you set the amount to `0.1 ETH` and confirm it in MetaMask, you can then track the successful transaction on Etherscan. In the Etherscan transaction log, you will see that the `fundMe` balance has increased by `0.1 ETH`. The `funders` array will register your address, and the mapping `addressToAmountFunded` will record the amount of ETH sent. ### Withdraw Function and Errors After funding the contract, we can initiate the `withdraw` function. This function can only be called by the owner; if a non-owner account attempts to withdraw, a gas estimation error will be thrown, and the function will revert. Upon successful withdrawal, the `fundMe` balance, the `addressToAmountFunded` mapping, and the `funders` array will all reset to zero. ### Conclusion In this lesson, we've explored the end-to-end process of deploying and interacting with a Solidity contract using Remix and MetaMask. We covered the deployment transaction, contract interaction, and how to handle successful transactions and potential errors. ### 🧑‍💻 Test yourself 1. 🧑‍💻 Interact with the `FundMe` contract on Remix and explore all possible outcomes that its functions can lead to.