testing private methods in C# with reflection

I wrote this class...

namespace PrivateMethodTesting.Models

{

   public class SummationScienceExperiment

   {

      public int DependentVariable { get; private set; }

      public int IndependentVariable { get; private set; }

      public double? DivisionCalculation { get; private set; }

      

      public SummationScienceExperiment(int ofStone, int ofClay)

      {

         DependentVariable = ofStone;

         IndependentVariable = ofClay;

         DivisionCalculation = craftDecimal(ofStone, ofClay);

      }

      

      public void Update(int ofClay)

      {

         IndependentVariable = ofClay;

         DivisionCalculation = craftDecimal(DependentVariable, ofClay);

      }

      

      private double? craftDecimal(int ofStone, int ofClay)

      {

         if (ofClay == 0) return null;

         return (double)ofStone/(double)ofClay;

      }

   }

}

 
 

...and then I wrote the following four tests around it. The last test uses reflection to test the private method.

using System;

using System.Reflection;

using Microsoft.VisualStudio.TestTools.UnitTesting;

using PrivateMethodTesting.Models;

namespace PrivateMethodTesting.Tests

{

   [TestClass]

   public class SummationScienceExperimentTests

   {

      [TestMethod]

      public void constructor_should_craft_a_decimal()

      {

         SummationScienceExperiment foo = new SummationScienceExperiment(5,2);

         Assert.AreEqual(5, foo.DependentVariable);

         Assert.AreEqual(2, foo.IndependentVariable);

         Assert.AreEqual(2.5, foo.DivisionCalculation);

      }

      

      [TestMethod]

      public void update_should_craft_a_decimal()

      {

         SummationScienceExperiment foo = new SummationScienceExperiment(5, 2);

         foo.Update(4);

         Assert.AreEqual(5, foo.DependentVariable);

         Assert.AreEqual(4, foo.IndependentVariable);

         Assert.AreEqual(1.25, foo.DivisionCalculation);

      }

      

      [TestMethod]

      public void may_divide_zero()

      {

         SummationScienceExperiment foo = new SummationScienceExperiment(0, 2);

         Assert.AreEqual(0, foo.DependentVariable);

         Assert.AreEqual(2, foo.IndependentVariable);

         Assert.AreEqual(0, foo.DivisionCalculation);

      }

      

      [TestMethod]

      public void may_not_divide_by_zero()

      {

         Type type = typeof(SummationScienceExperiment);

         var infos = type.GetMethods(BindingFlags.NonPublic|BindingFlags.Instance);

         MethodInfo info = infos[3];

         SummationScienceExperiment foo = new SummationScienceExperiment(5, 2);

         Assert.AreEqual(info.Invoke(foo, new object[] { foo.DependentVariable, 0 }),null);

      }

   }

}