Reuse connection among DbContext instances in unit test - entity-framework

Question

I'm trying to setup some unit tests using EntityFramework 5, SQL Server Compact 4 and Xunit.
I'm using different context instances because I'm testing a ASP MVC app and I need to test the behavior of some update operations over detached entities.
[Fact, AutoRollback]
public void TestConnection()
{
using (var connection = this.GetDbConnection())
{
using (var context = new MyContext(connection, false))
{
// Do database stuff
}
using (var context = new MyContext(connection, false))
{
// Do database stuff
}
}
}
public DbConnection GetDbConnection()
{
string dataSource = "|DataDirectory|\\MyDb.sdf";
var sqlBuilder = new SqlCeConnectionStringBuilder();
sqlBuilder.DataSource = dataSource;
return new SqlCeConnection(sqlBuilder.ToString());
}
This gives me the following error:
System.Data.EntityException : The underlying provider failed on Open.
System.InvalidOperationException : The connection object can not be enlisted in transaction scope.
I know I can't open multiple DbContext instances inside a TransactionScope (that is probably what Xunit does when you put a FallbackAttribute in your method), so that's why I'm creating the connection beforehand.
If I try to open the connection myself, it still does not work:
using (var connection = this.GetDbConnection())
{
connection.Open();
using (var context = new MyContext(connection, false))
{
I get the following exception:
System.ArgumentException : EntityConnection can only be constructed with a closed DbConnection.
Does any one know how to solve that issue?
EDIT
The test classes that deal with the Db extend a "DomainFactsBase" where the database is initialized as the following:
public DomainFactsBase()
{
Database.SetInitializer(new DropCreateDatabaseIfModelChanges<MyContext>());
using (var context = new MyContext(GetDbConnection(), true))
context.Database.Initialize(false);
}
EDIT
I can sucessfully run tests with autorollback when I create only one context instance. This was accomplished following the instructions in this article. I have a extension method:
public static void OpenConnection(this DbContext context)
{
((IObjectContextAdapter)context).ObjectContext.Connection.Open();
}
And I call it right after creating the context in the tests:
[Fact, AutoRollback]
public void SomeFact()
{
using (var context = new MyContext())
{
context.OpenConnection();
// Do stuff
}
}
That work with no problems. They arise when I try to open the context more than once in the same fact (with AutoRollback enabled), as I examplified in the beginning.

Answer 1

Initialize the database outside of the test. You can do this inside of the test class's constructor.
public MyTestClass()
{
using (var db = new MyContext(GetDbConnection(), true))
{
db.Database.Initialize(false);
}
}