Mocktest a library method that consumes WCF operation

[Test]
public void GetUsersTest()
{
    var fakeWcfClient = Isolate.Fake.Instance<WcfClient>();
    Isolate.WhenCalled(() => fakeWcfClient.GetUsers())
        .WillReturn(new List<User> { new User("TestUser1"), new User("TestUser2") });
    Isolate.Swap.NextInstance<WcfClient>().With(fakeWcfClient);

    UsersProvider provider = new UsersProvider();

    var users = provider.GetUsersFromWcf();

    Assert.AreEqual(2, users.Count);
}

public class UsersProvider
{
    public List<User> GetUsersFromWcf()
    {
        List<User> users;

        using (var client = new WcfClient())
        {
            users = client.GetUsers();
        }

        return users;
    }
}