public void Dispose()
{
using (var conn = OpenConnection())
{
var cmd = new NpgsqlCommand("SELECT 1", conn);
cmd.Dispose();
Assert.That(() => cmd.ExecuteScalar(), Throws.Exception.TypeOf<ObjectDisposedException>());
Assert.That(() => cmd.ExecuteNonQuery(), Throws.Exception.TypeOf<ObjectDisposedException>());
Assert.That(() => cmd.ExecuteReader(), Throws.Exception.TypeOf<ObjectDisposedException>());
Assert.That(() => cmd.Prepare(), Throws.Exception.TypeOf<ObjectDisposedException>());
}
}