public class GetByIdTests : BaseTest
{
    protected Mock<IProductRepository> Repository { get; private set; }

    protected ProductLogic Create()
    {
        Repository = new Mock<IProductRepository>();

        return new ProductLogic(new Lazy<IProductRepository>(() => Repository.Object));
    }

    [Fact]
    public void Return_Product_From_Repository()
    {
        var logic = Create();

        var product = Builder<Product>.CreateNew().Build();

        Repository.Setup(r => r.GetById(It.IsAny<int>()))
            .Returns(product);

        var result = logic.GetById(10);

        Assert.NotNull(result);
        Assert.True(result.Success);
        Assert.Equal(product, result.Value);
        Assert.NotNull(result.Errors);
        Assert.Equal(0, result.Errors.Count());

        Repository.Verify(r => r.GetById(10), Times.Once());
    }

    [Fact]
    public void Return_Error_When_Product_Not_Exist()
    {
        var logic = Create();

        Repository.Setup(r => r.GetById(It.IsAny<int>()))
            .Returns((Product)null);

        var result = logic.GetById(10);

        Assert.NotNull(result);
        Assert.False(result.Success);
        Assert.Null(result.Value);
        Assert.NotNull(result.Errors);
        Assert.Equal(1, result.Errors.Count());

        var error = result.Errors.First();

        Assert.Equal(string.Empty, error.PropertyName);
        Assert.Equal("Nie ma produktu o id 10.", error.Message);

        Repository.Verify(r => r.GetById(10), Times.Once());
    }
}