Basic unit testing with .NET and Moq
I spent some more time looking at the test package that comes with Visual Studio 2010 and it looks pretty basic; mainly focusing on assertions. But what if I need to test more than assertions? That is where mocking comes into play. With mocking, you can test how your objects will interact with other objects. If I want to test my code against a Dao without actually hitting a database (which is what you want to do), then I would need to fake that connection and mock the Dao. Mocking the Dao will allow me to return any result that I would like from the operations based on the input.
For this quick example I will be using a third-party mocking library called Moq. You can find it on GitHub here.
I started by creating a very basic Dao:
using System; using System.Collections; namespace QuickTesting { /// /// Fake Dao /// public class DBClass { /// /// Local storage object /// private Hashtable hashTable = new Hashtable(); /// /// Public accessor of local storage object /// public Hashtable DataBase { get { return this.hashTable; } } public DBClass() { } /// /// Save the object in storage /// ///Object to save ///Success of storing public virtual bool Save(PlainObject po) { this.hashTable.Add(po.Id, po); return this.hashTable.ContainsKey(po.Id); } /// /// Update the object by replacement /// ///Object to update ///Success of update public virtual bool Update(PlainObject po) { this.hashTable[po.Id] = po; return this.hashTable.ContainsKey(po.Id); } /// /// Removes the object from storage /// ///The id of the object to remove /// Success of removal public virtual bool Delete(int Id) { this.hashTable.Remove(Id); return this.hashTable.ContainsKey(Id); } } }
Now I need an object to test against my quick Dao:
using System; namespace QuickTesting { /// /// Simple object to store values /// public class PlainObject { public int Id { get; set; } public string Name { get; set; } private DBClass dbClass; /// /// Constructor injection of the Dao object /// /// public PlainObject(DBClass dbClass) { if (dbClass == null) throw new ArgumentNullException("DBClass is null"); this.dbClass = dbClass; } /// /// Save the current object data to the database /// /// Success of save public bool SaveToDb() { return this.dbClass.Save(this); } /// /// Update the current object data in the database /// /// Success of update public bool UpdateToDb() { return this.dbClass.Update(this); } /// /// Remove the current object from the database /// /// Success of removal public bool RemoveFromDb() { return this.dbClass.Delete(this.Id); } } }
I am using constructor injection to give my PlainObject access to the Dao; now I need to test that is works correctly. The first test will test the DBClass and the PlainObject themselves to be sure that I don't have any problems before I try to mock the DBClass.
The second test will test the PlainObject against a mocked DBClass and let me know that I am getting the expected results and that I am exercising the correct code.
using System; using Moq; using Microsoft.VisualStudio.TestTools.UnitTesting; using QuickTesting; namespace QuickTestingTestProject { /// /// Quick test using mock objects /// [TestClass] public class QuickMockUnitTest { #region Mock Object Testing [TestMethod()] public void TestDBClass() { // Test both concrete classes DBClass dbClass = new DBClass(); PlainObject po = new PlainObject(dbClass); po.Id = 1; po.Name = "Homer"; // Verify that the object saved successfully Assert.IsTrue(po.SaveToDb()); // Verify that the object added is there and is the correct object Assert.AreEqual(dbClass.DataBase.Count, 1); Assert.ReferenceEquals(dbClass.DataBase[1], po); } [TestMethod()] public void MockTestOne() { var dbClassMock = new Mock(); // Create the classs to be tested PlainObject poHomer = new PlainObject(dbClassMock.Object); poHomer.Id = 1; poHomer.Name = "Homer"; PlainObject poMarge = new PlainObject(dbClassMock.Object); poMarge.Id = 2; poMarge.Name = "Marge"; // Mock the DBClass return values. Setting a different result based on // the object being passed into it. This helps to test different code paths // based on results. dbClassMock.Setup(db => db.Save(poMarge)).Returns(false); dbClassMock.Setup(db => db.Save(poHomer)).Returns(true); // The mock will return false no matter what for the poMarge Object Assert.IsFalse(poMarge.SaveToDb()); // The mock will return true no matter what for the poHomer Object Assert.IsTrue(poHomer.SaveToDb()); // Verify that save was called for all objects dbClassMock.Verify(v => v.Save(It.IsAny()), Times.Exactly(2)); // And verify that it was called for each object individually as well dbClassMock.Verify(v => v.Save(poMarge), Times.Once()); dbClassMock.Verify(v => v.Save(poHomer), Times.Once()); } #endregion } }
For the next post I will get more into mocking and show you just how powerful and easy it can be. Once again all of the code examples can be found on GitHub.
Note: If you are unfamiliar with constructor injection you can read a decent description about it here.
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