Property tests of string variables in Solidity

ChangeByte.sol

pragma solidity >=0.7.0 <0.8.0;

contract ChangeByte {
    bytes8 text = 'abcdefgh';
    
    // 0x6162636465666768
    function getText() public view returns(bytes8) {
        return text;
    }
    
    // 0x61
    function change1() public view returns(bytes1) {
        return bytes1(text);
    }
    
    // 0x6162
    function change2() public view returns(bytes2) {
        return bytes2(text);
    }
    
    function fixed2dynamic() public view returns(bytes memory) {
        bytes memory newText = new bytes(text.length);
        for (uint i = 0; i < text.length; i++) {
            newText[i] = text[i];
        }
        return newText;
    }
}

PayTest.sol

pragma solidity >=0.7.0 <0.8.0;

contract PayTest {
    
    // Ether will be transferred from account to contract
    function pay() public payable {
        
    }
    
    // "this" will be pointed to the contract
    function getThis() public view returns(address) {
        return address(this);
    }
    
    function getBalance() public view returns(uint) {
        return address(this).balance;
    }
    
    // This address could be either account or deployed contracts
    function getBalanceAcc() public view returns(uint) {
        address account = 0x4B20993Bc481177ec7E8f571ceCaE8A9e22C02db;
        return account.balance;
    }
    
    function transfer() public payable {
        address payable acc = 0x78731D3Ca6b7E34aC0F824c42a7cC18A495cabaB; // Transfer from current account to this one
        acc.transfer(msg.value);
    }
}

StringByte.sol

pragma solidity >=0.7.0 <0.8.0;

/**
 * Some String and Byte type test
 */
contract StringByte {
    string private text1 = 'abcdefgh';
    
    // This will not cost ether with the "view" modifier
    function getString() public view returns(string memory) {
        return text1;
    }
    
    function getLength() public view returns(uint) {
        // return text1.length; -> Can't do This
        return bytes(text1).length;
    }
    
    // This will cost ether as it modifies values on the chain
    function setValue(string memory newStr) public {
        text1 = newStr;
    }
    
    function getChar(uint idx) public view returns(bytes1) {
        if (idx >= 0 && idx < getLength()) {
            // return text1[0]; -> Can't do this
            return bytes(text1)[idx];
        }
        else {
            return '';
        }
    }
    
    function setChar(uint idx, bytes1 a) public {
        if (idx >= 0 && idx < getLength()) {
            bytes(text1)[idx] = a;
        }
    }
}