Claude 3.7

write me some unit tests for this contract

// SPDX-License-Identifier: LGPL-3.0-only /* solhint-disable one-contract-per-file */ pragma solidity >=0.7.0 <0.9.0; / * @title IProxy - Helper interface to access the singleton address of the Proxy on-chain.  * @author Richard Meissner - @rmeissner  */ interface IProxy {     function masterCopy() external view returns (address); } / * @title SafeProxy - Generic proxy contract allows to execute all transactions applying the code of a master contract.  * @author Stefan George - <stefan@gnosis.io>  * @author Richard Meissner - <richard@gnosis.io>  */ contract SafeProxy {     // Singleton always needs to be first declared variable, to ensure that it is at the same location in the contracts to which calls are delegated.     // To reduce deployment costs this variable is internal and needs to be retrieved via getStorageAt    address internal singleton;     /     * @notice Constructor function sets address of singleton contract.      * @param _singleton Singleton address.      */     constructor(address _singleton) {         require(_singleton != address(0), "Invalid singleton address provided");         singleton = _singleton;     }     /// @dev Fallback function forwards all transactions and returns all received return data.     fallback() external payable {         // Note that this assembly block is intentionally not marked as memory-safe. First of all, it isn't memory         // safe to begin with, and turning this into memory-safe assembly would just make it less gas efficient.         // Additionally, we noticed that converting this to memory-safe assembly had no affect on optimizations of other         // contracts (as it always gets compiled alone in its own compilation unit anyway).         /* solhint-disable no-inline-assembly */         assembly {             let _singleton := sload(0)             // 0xa619486e == bytes4(keccak256("masterCopy()")). The value is right padded to 32-bytes with 0s             if eq(calldataload(0), 0xa619486e00000000000000000000000000000000000000000000000000000000) {                 // We mask the singleton address when handling the masterCopy() call to ensure that it is correctly                 // ABI-encoded. We do this by shifting the address left by 96 bits (or 12 bytes) and then storing it in                 // memory with a 12 byte offset from where the return data starts. Note that we intentionally** only                 // do this for the masterCopy() call, since the EVM DELEGATECALL opcode ignores the most-significant                 // 12 bytes from the address, so we do not need to make sure the top bytes are cleared when proxying                 // calls to the singleton. This saves us a tiny amount of gas per proxied call.                 mstore(0x0c, shl(96, _singleton))                 return(0, 0x20)             }             calldatacopy(0, 0, calldatasize())             let success := delegatecall(gas(), _singleton, 0, calldatasize(), 0, 0)             returndatacopy(0, 0, returndatasize())             if iszero(success) {                 revert(0, returndatasize())             }             return(0, returndatasize())         }         /* solhint-enable no-inline-assembly */     } }