I crate domain project to store dbml file and several domain classes. I create unit test project to test CRUD operation. I reference domain project to the test project. 

I declare the db context in the unit test, in the test method `I try to access method db.SubmitChanges(); but It is not accessible`.

But when the unit test file stored in the domain project, the db method is accessible. 

```
[TestFixture]
class CustomerRepositoryTest
{
    NorthWindDataContext db = new NorthWindDataContext();
    Customer _customer = null;

    [SetUp]
    public void SetUp() {
        //initialize customer
    }

    [Test]
    public void Should_able_to_get_data_when_data_is_inserted()
    {
        db.Customers.InsertOnSubmit(_customer);
        db.SubmitChanges();

        Customer customer = db.Customers.FirstOrDefault(c => c.CustomerID == _customer.CustomerID);

        Assert.AreEqual(customer.CustomerID.Trim(), _customer.CustomerID);
        Assert.AreEqual(customer.ContactName.Trim(), _customer.ContactName);
    }

    [TearDown]
    public void After()
    {
        db.Customers.DeleteOnSubmit(_customer);
        db.SubmitChanges();
    }
}

```

Let me know how to fix this.

**EDIT**:

```
Error   1   'AppProject.Domain.NorthWindDataContext' does not contain a definition for 'SubmitChanges' and no extension method 'SubmitChanges' accepting a first argument of type 'AppProject.Domain.NorthWindDataContext' could be found (are you missing a using directive or an assembly reference?) D:\tutorial\dotNET\LINQtoSQL\AppProject.Spec\Should_insert_customer.cs  40  16  AppProject.Spec

```