Created using remix-ide: Realtime Ethereum Contract Compiler and Runtime. Load this file by pasting this gists URL or ID at https://remix.ethereum.org/#version=soljson-v0.5.1+commit.c8a2cb62.js&optimize=false&gist=

00_MyContract.sol

pragma solidity 0.5.1;

contract MyContract {
    enum State { Waiting, Ready, Active }
    
    State public state;
    
    constructor() public {
        state = State.Waiting;
    }
    
    function activate() public {
        state = State.Active;
    }
    
    function isActive() public view returns(bool) {
        return state == State.Active;
    }
}

01_MyContract.sol

pragma solidity 0.5.1;

contract MyContract {
    
    //Person[] public people_original;
    uint256 public peopleCount = 0;
    mapping(uint => Person) public people;
    
    struct Person {
        uint _id;
        string _firstname;
        string _lastname;
    }
    
    // function addPerson(string memory _firstName, string memory _lastname) public {
    //     people.push(Person(_firstName, _lastname));
    //     peopleCount += 1;
    // }
    
    function addPerson(string memory _firstName, string memory _lastname) public {
        peopleCount += 1;
        people[peopleCount] = Person(peopleCount, _firstName, _lastname);
    }
    
    
}

02_MyContract.sol

pragma solidity 0.5.1;

contract MyContract {
    uint256 public peopleCount = 0;
    mapping(uint => Person) public people;
    
    address owner;
    
    modifier onlyOwner() {
        // msg es un global keyword, the function metadata that is passed in
        // Tells the account/address who calls the function
        // require: si evalua a true pasa OK, si evalua a false tira un error. Es como assertion
        require(msg.sender == owner);
        _;
    }
    
    constructor() public {
        owner = msg.sender;
    }
    
    struct Person {
        uint _id;
        string _firstName;
        string _lastName;
    }
    
    // OJO antes de las llaves se aplica el modificador onlyOwner, ejecuta el codigo de arriba
    //Que permite solo al dueño pasar por la funcion addPerson.
    function addPerson(
        string memory _firstName,
        string memory _lastName
    ) public onlyOwner {
    //function addPerson(string memory _firstName, string memory _lastName) public {
        implementCount();
        people[peopleCount] = Person(peopleCount, _firstName, _lastName);
    }
    
    function implementCount() internal {
        peopleCount += 1;
    }
}

03_MyContract.sol

pragma solidity 0.5.1;

contract MyContract {
    uint256 public peopleCount = 0;
    mapping(uint => Person) public people;
    uint256 openingTime = 1586193260 + 60;
    address owner;
    
    modifier onlyWhileOpen() {
        // block es otra variable global disponible en solidity
        require(block.timestamp >= openingTime);
        _;
    }
    
    constructor() public {
        owner = msg.sender;
    }
    
    struct Person {
        uint _id;
        string _firstName;
        string _lastName;
    }
    
    // OJO antes de las llaves se aplica el modificador onlyOwner, ejecuta el codigo de arriba
    //Que permite solo al dueño pasar por la funcion addPerson.
    function addPerson(
        string memory _firstName,
        string memory _lastName
    ) public onlyWhileOpen
    {
    //function addPerson(string memory _firstName, string memory _lastName) public {
        implementCount();
        people[peopleCount] = Person(peopleCount, _firstName, _lastName);
    }
    
    function implementCount() internal {
        peopleCount += 1;
    }
}

04_MyContract.sol

pragma solidity 0.5.1;

contract MyContract {
    
    mapping (address => uint256) public balances;
    address payable wallet;
    
    //indexed enables you to filter events for certain buyers
    event Purchase (
        address indexed _buyer,
        uint256 _amount
    );
    
    constructor(address payable _wallet) public {
        wallet = _wallet;
    }
    
    // external modifier, SOLO se puede llamar desde afuera
    function() external payable {
        buyToken();
    }
    
    // Agregar modificador payable para avisar que la funcion va a aceptar ether
    function buyToken() public payable {
        // buy a token
        balances[msg.sender] += 1;
        // send ether to the wallet
        wallet.transfer(msg.value);
        // trigger event
        emit Purchase(msg.sender, 1);
    }
}

05_MyContract.sol

// this line is added to create a gist. Empty file is not allowed.

1_Storage.sol

pragma solidity >=0.4.22 <0.7.0;

/**
 * @title Storage
 * @dev Store & retreive value in a variable
 */
contract Storage {

    uint256 number;

    /**
     * @dev Store value in variable
     * @param num value to store
     */
    function store(uint256 num) public {
        number = num;
    }

    /**
     * @dev Return value 
     * @return value of 'number'
     */
    function retreive() public view returns (uint256){
        return number;
    }
}

2_Owner.sol

pragma solidity >=0.4.22 <0.7.0;

/**
 * @title Owner
 * @dev Set & change owner
 */
contract Owner {

    address private owner;
    
    // event for EVM logging
    event OwnerSet(address indexed oldOwner, address indexed newOwner);
    
    // modifier to check if caller is owner
    modifier isOwner() {
        // If the first argument of 'require' evaluates to 'false', execution terminates and all
        // changes to the state and to Ether balances are reverted.
        // This used to consume all gas in old EVM versions, but not anymore.
        // It is often a good idea to use 'require' to check if functions are called correctly.
        // As a second argument, you can also provide an explanation about what went wrong.
        require(msg.sender == owner, "Caller is not owner");
        _;
    }
    
    /**
     * @dev Set contract deployer as owner
     */
    constructor() public {
        owner = msg.sender; // 'msg.sender' is sender of current call, contract deployer for a constructor
        emit OwnerSet(address(0), owner);
    }

    /**
     * @dev Change owner
     * @param newOwner address of new owner
     */
    function changeOwner(address newOwner) public isOwner {
        emit OwnerSet(owner, newOwner);
        owner = newOwner;
    }

    /**
     * @dev Return owner address 
     * @return address of owner
     */
    function getOwner() external view returns (address) {
        return owner;
    }
}

3_Ballot.sol

pragma solidity >=0.4.22 <0.7.0;

/** 
 * @title Ballot
 * @dev Implements voting process along with vote delegation
 */
contract Ballot {
   
    struct Voter {
        uint weight; // weight is accumulated by delegation
        bool voted;  // if true, that person already voted
        address delegate; // person delegated to
        uint vote;   // index of the voted proposal
    }

    struct Proposal {
        // If you can limit the length to a certain number of bytes, 
        // always use one of bytes1 to bytes32 because they are much cheaper
        bytes32 name;   // short name (up to 32 bytes)
        uint voteCount; // number of accumulated votes
    }

    address public chairperson;

    mapping(address => Voter) public voters;

    Proposal[] public proposals;

    /** 
     * @dev Create a new ballot to choose one of 'proposalNames'.
     * @param proposalNames names of proposals
     */
    constructor(bytes32[] memory proposalNames) public {
        chairperson = msg.sender;
        voters[chairperson].weight = 1;

        for (uint i = 0; i < proposalNames.length; i++) {
            // 'Proposal({...})' creates a temporary
            // Proposal object and 'proposals.push(...)'
            // appends it to the end of 'proposals'.
            proposals.push(Proposal({
                name: proposalNames[i],
                voteCount: 0
            }));
        }
    }
    
    /** 
     * @dev Give 'voter' the right to vote on this ballot. May only be called by 'chairperson'.
     * @param voter address of voter
     */
    function giveRightToVote(address voter) public {
        require(
            msg.sender == chairperson,
            "Only chairperson can give right to vote."
        );
        require(
            !voters[voter].voted,
            "The voter already voted."
        );
        require(voters[voter].weight == 0);
        voters[voter].weight = 1;
    }

    /**
     * @dev Delegate your vote to the voter 'to'.
     * @param to address to which vote is delegated
     */
    function delegate(address to) public {
        Voter storage sender = voters[msg.sender];
        require(!sender.voted, "You already voted.");
        require(to != msg.sender, "Self-delegation is disallowed.");

        while (voters[to].delegate != address(0)) {
            to = voters[to].delegate;

            // We found a loop in the delegation, not allowed.
            require(to != msg.sender, "Found loop in delegation.");
        }
        sender.voted = true;
        sender.delegate = to;
        Voter storage delegate_ = voters[to];
        if (delegate_.voted) {
            // If the delegate already voted,
            // directly add to the number of votes
            proposals[delegate_.vote].voteCount += sender.weight;
        } else {
            // If the delegate did not vote yet,
            // add to her weight.
            delegate_.weight += sender.weight;
        }
    }

    /**
     * @dev Give your vote (including votes delegated to you) to proposal 'proposals[proposal].name'.
     * @param proposal index of proposal in the proposals array
     */
    function vote(uint proposal) public {
        Voter storage sender = voters[msg.sender];
        require(sender.weight != 0, "Has no right to vote");
        require(!sender.voted, "Already voted.");
        sender.voted = true;
        sender.vote = proposal;

        // If 'proposal' is out of the range of the array,
        // this will throw automatically and revert all
        // changes.
        proposals[proposal].voteCount += sender.weight;
    }

    /** 
     * @dev Computes the winning proposal taking all previous votes into account.
     * @return winningProposal_ index of winning proposal in the proposals array
     */
    function winningProposal() public view
            returns (uint winningProposal_)
    {
        uint winningVoteCount = 0;
        for (uint p = 0; p < proposals.length; p++) {
            if (proposals[p].voteCount > winningVoteCount) {
                winningVoteCount = proposals[p].voteCount;
                winningProposal_ = p;
            }
        }
    }

    /** 
     * @dev Calls winningProposal() function to get the index of the winner contained in the proposals array and then
     * @return winnerName_ the name of the winner
     */
    function winnerName() public view
            returns (bytes32 winnerName_)
    {
        winnerName_ = proposals[winningProposal()].name;
    }
}

4_Ballot_test.sol

pragma solidity >=0.4.22 <0.7.0;
import "remix_tests.sol"; // this import is automatically injected by Remix.
import "./3_Ballot.sol";

contract BallotTest {
   
    bytes32[] proposalNames;
   
    Ballot ballotToTest;
    function beforeAll () public {
        proposalNames.push(bytes32("candidate1"));
        ballotToTest = new Ballot(proposalNames);
    }
    
    function checkWinningProposal () public {
        ballotToTest.vote(0);
        Assert.equal(ballotToTest.winningProposal(), uint(0), "proposal at index 0 should be the winning proposal");
        Assert.equal(ballotToTest.winnerName(), bytes32("candidate1"), "candidate1 should be the winner name");
    }
    
    function checkWinninProposalWithReturnValue () public view returns (bool) {
        return ballotToTest.winningProposal() == 0;
    }
}

MyContract.sol

pragma solidity 0.5.1;

contract MyContract {
    string public stringValue = "myString";
    bool public myBool = true;
    int public myInt = -1;
    
    uint public myUInt = 1;
    uint8 public myuint8 = 8;
    
    uint256 public myuint256 = 99999;
    
}