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Escrow.sol

pragma solidity >=0.4.1 <0.6.0;

contract Escrow {
    uint balance;
    address public buyer;
    address public seller;
    address private escrow;
    uint private start;
    bool buyerOk;
    bool sellerOk;
    
    constructor (address buyer_address, address seller_address) public {
        // this is the constructor function that runs ONCE upon initialization
        buyer = buyer_address;
        seller = seller_address;
        escrow = msg.sender;
        start = now; //now is an alias for block.timestamp, not really "now"
    }
    
    function accept() public {
        if (msg.sender == buyer){
            buyerOk = true;
        }
        if (msg.sender == seller){
            sellerOk = true;
        }
        if (buyerOk && sellerOk){
            payBalance();
        } else if (buyerOk && !sellerOk && now > start + 30 days) {
            // Freeze 30 days before release to buyer. The customer has to remember to call this method after freeze period.
            selfdestruct(buyer);
        }
    }
        
    function payBalance() private {
        // send seller the balance
        require(seller.send(balance));
        balance = 0;
    }
    
    function deposit() public payable {
        if (msg.sender == buyer) {
            balance += msg.value;
        }
    }
    
    function cancel() public {
        if (msg.sender == buyer){
            buyerOk = false;
        } else if (msg.sender == seller){
            sellerOk = false;
        }
        // if both buyer and seller would like to cancel, money is returned to buyer 
        if (!buyerOk && !sellerOk){
            selfdestruct(buyer);
        }
    }
    
    function kill() public {
        if (msg.sender == escrow) {
            selfdestruct(buyer);
        }
    }
}

escrow_test.sol

pragma solidity >=0.4.22 <0.6.0;
import "remix_tests.sol"; // this import is automatically injected by Remix.
import "./Escrow.sol";

contract escrow_test {
    Escrow escrow;
    address buyerAddress = 0xa978c937cB8A7fC57407B6B5C45741C579Ca3A11;
    address sellerAddress = 0x4B0897b0513fdC7C541B6d9D7E929C4e5364D2dB;
    
    function beforeAll () public {
        escrow = new Escrow(buyerAddress, sellerAddress);
    }
    
    function checkAccept () public{
        escrow.accept();
    }
}

test_test.sol

pragma solidity >=0.4.0 <0.6.0;
      import "remix_tests.sol"; // this import is automatically injected by Remix.

      // file name has to end with '_test.sol'
      contract test_1 {

        function beforeAll() public {
          // here should instantiate tested contract
          Assert.equal(uint(4), uint(3), "error in before all function");
        }

        function check1() public {
          // use 'Assert' to test the contract
          Assert.equal(uint(2), uint(1), "error message");
          Assert.equal(uint(2), uint(2), "error message");
        }

        function check2() public view returns (bool) {
          // use the return value (true or false) to test the contract
          return true;
        }
      }

    contract test_2 {

      function beforeAll() public {
        // here should instantiate tested contract
        Assert.equal(uint(4), uint(3), "error in before all function");
      }

      function check1() public {
        // use 'Assert' to test the contract
        Assert.equal(uint(2), uint(1), "error message");
        Assert.equal(uint(2), uint(2), "error message");
      }

      function check2() public view returns (bool) {
        // use the return value (true or false) to test the contract
        return true;
      }
    }