Custom RoleProvider Error - Using Article To Learn

I'm trying to use this article to learn about custom roleproviders, but I'm getting this error:

Could not load type 'TestRoles.SimpleRoleProvider'.

The relevant section from my web.config:

<roleManager enabled="true" defaultProvider="SimpleRoleProvider">
<providers>
<add name="SimpleRoleProvider" type="TestRoles.SimpleRoleProvider"/>
</providers>
</roleManager>

The RolesProvider.cs class:

public class TestRoles{
public class SimpleRoleProvider : RoleProvider
{
public override string[] GetRolesForUser(string username)
{
List<string> roles = new List<string>();
roles.Add("Guest");
if (username.Equals("Dave"))
roles.Add("Admin");
return roles.ToArray();
}
}
}

From this error, it seems like it can't find the RoleProvider.