Star date: 2010.023
A couple months ago I wrote this article explaining why I think it is reasonable for unit tests to hit a real database. Subsequently, I wrote a follow up article describing some techniques for rolling back your database to its original state after each test. In that article I found that just using simple transactions did not solve the problem because you need access to all database connections being used, and they all have to be rolled back. I have since found a way around this problem using distributed transactions.
With the Microsoft Distributed Transaction Coordinator (MSDTC) the activity over multiple connections can be lumped into a single transaction using the TransactionScope class. MSDTC needs to be running for this to work, but since this is just for unit tests it doesn't need to be enabled on your production environment.
In order to use the TransactionScope class your project will need a reference to System.Transactions. Here's a sample unit test using MSTest and Entity Framework where the database is altered with multiple connections within a transaction and then the changes are rolled back:
Imports System.Transactions
Imports System
Imports System.Text
Imports System.Collections.Generic
Imports Microsoft.VisualStudio.TestTools.UnitTesting
<TestClass()> _
Public Class UnitTestSample
<TestMethod()> _
Public Sub ProofOfConceptTest()
Using New TransactionScope
Dim conn1 As New DataTestEntities
Dim conn2 As New DataTestEntities
Dim row1 As New Users With {.userName = "user1", .password = "pass"}
Dim row2 As New Users With {.userName = "user2", .password = "pass"}
conn1.AddToUsers(row1)
conn2.AddToUsers(row2)
conn1.SaveChanges()
conn2.SaveChanges()
Dim conn3 As New DataTestEntities
Assert.AreEqual(conn3.Users.Count, 6)
End Using
End Sub
End Class
Alternatively, if you want every test method inside a test class to be within its own TransactionScope without adding a Using block to every single test, you can use the initialization and cleanup methods like this:
Imports System.Transactions
Imports System
Imports System.Text
Imports System.Collections.Generic
Imports Microsoft.VisualStudio.TestTools.UnitTesting
<TestClass()> _
Public Class UnitTestSample
Private _transaction As TransactionScope
<TestInitialize()> _
Public Sub Setup()
_transaction = New TransactionScope
End Sub
<TestCleanup()> _
Public Sub TearDown()
_transaction.Dispose()
End Sub
<TestMethod()> _
Public Sub ProofOfConceptTest()
Dim conn1 As New DataTestEntities
Dim conn2 As New DataTestEntities
Dim row1 As New Users With {.userName = "user1", .password = "pass"}
Dim row2 As New Users With {.userName = "user2", .password = "pass"}
conn1.AddToUsers(row1)
conn2.AddToUsers(row2)
conn1.SaveChanges()
conn2.SaveChanges()
Dim conn3 As New DataTestEntities
Assert.AreEqual(conn3.Users.Count, 6)
End Sub
End Class
As long as the use of MSDTC is an option, I have found this method to be far better than any of those described in the last article. It guarantees that the state or your database is maintained and is extremely fast (at least on small amounts of data).