private void button1_Click(object sender, EventArgs e)
        {
            int a    = Convert.ToInt32(textBox1.Text);
            int b    = Convert.ToInt32(textBox3.Text);
            int suma = CalculadoraFacade.Suma(a, b);

            textBox2.Text = suma.ToString();
        }
 public void TestSuma()
 {
     Assert.AreEqual(6, CalculadoraFacade.Suma(2, 4));
 }