public virtual void Close()
        {
            using (HsqlConnection testSubject = new HsqlConnection())
            {
                Assert.That(testSubject.State == ConnectionState.Closed);

                testSubject.Open();

                Assert.That(testSubject.State == ConnectionState.Open);

                testSubject.Close();

                Assert.That(testSubject.State == ConnectionState.Closed);

                testSubject.Close();

                Assert.That(testSubject.State == ConnectionState.Closed);
            }
        }