Simple class of Human.

Human.cs

public class Human
{
    public int Energy { get; private set; }
    public bool Tired { get; private set; }

    public void Eat(int calory)
    {
        Energy += calory;
    }

    public void Work(int calory)
    {
        Energy -= calory;

        if (Energy < 0)
        {
            Energy = 0;
            Tired = true;
        }
    }

    public void Rest()
    {
        Tired = false;
    }
}

HumanClassTest.cs

[TestClass]
public class HumanClassTest
{
    [TestMethod]
    public void TooMuchWorkAndBecomeTired()
    {
        var human = new Human();
        human.Eat(100);

        human.Work(200);

        Assert.AreEqual(true, human.Tired);
        Assert.AreEqual(0, human.Energy);
    }

    [TestMethod]
    public void EatSomethingAndEnergyIncreased()
    {
        var human = new Human();
        var calory = 100;
        var beginEnergy = human.Energy;

        human.Eat(calory);

        var endEnergy = human.Energy;

        Assert.AreEqual(calory, endEnergy - beginEnergy);
    }

    [TestMethod]
    public void AfterRestNotTiredAgain()
    {
        var human = new Human();
        human.Work(100);

        Assert.AreEqual(true, human.Tired);

        human.Rest();

        Assert.AreEqual(false, human.Tired);
    } 
}