test_cursor.py

#!/usr/bin/env python

# test_cursor.py - unit test for cursor attributes
#
# Copyright (C) 2010-2019 Daniele Varrazzo  <daniele.varrazzo@gmail.com>
# Copyright (C) 2020-2021 The Psycopg Team
#
# psycopg2 is free software: you can redistribute it and/or modify it
# under the terms of the GNU Lesser General Public License as published
# by the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# In addition, as a special exception, the copyright holders give
# permission to link this program with the OpenSSL library (or with
# modified versions of OpenSSL that use the same license as OpenSSL),
# and distribute linked combinations including the two.
#
# You must obey the GNU Lesser General Public License in all respects for
# all of the code used other than OpenSSL.
#
# psycopg2 is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
# License for more details.

import gc
import sys
import time
import ctypes
import pickle
import psycopg2
import psycopg2.extensions
import unittest
from datetime import date
from decimal import Decimal
from weakref import ref
from .testutils import (ConnectingTestCase, skip_before_postgres,
    skip_if_no_getrefcount, slow, skip_if_no_superuser,
    skip_if_windows, skip_if_crdb, crdb_version)

import psycopg2.extras


class CursorTests(ConnectingTestCase):

    def test_close_idempotent(self):
        cur = self.conn.cursor()
        cur.close()
        cur.close()
        self.assert_(cur.closed)

    def test_empty_query(self):
        cur = self.conn.cursor()
        self.assertRaises(psycopg2.ProgrammingError, cur.execute, "")
        self.assertRaises(psycopg2.ProgrammingError, cur.execute, " ")
        self.assertRaises(psycopg2.ProgrammingError, cur.execute, ";")

    def test_executemany_propagate_exceptions(self):
        conn = self.conn
        cur = conn.cursor()
        cur.execute("create table test_exc (data int);")

        def buggygen():
            yield 1 // 0

        self.assertRaises(ZeroDivisionError,
            cur.executemany, "insert into test_exc values (%s)", buggygen())
        cur.close()

    def test_mogrify_unicode(self):
        conn = self.conn
        cur = conn.cursor()

        # test consistency between execute and mogrify.

        # unicode query containing only ascii data
        cur.execute("SELECT 'foo';")
        self.assertEqual('foo', cur.fetchone()[0])
        self.assertEqual(b"SELECT 'foo';", cur.mogrify("SELECT 'foo';"))

        conn.set_client_encoding('UTF8')
        snowman = "\u2603"

        def b(s):
            if isinstance(s, str):
                return s.encode('utf8')
            else:
                return s

        # unicode query with non-ascii data
        cur.execute(f"SELECT '{snowman}';")
        self.assertEqual(snowman.encode('utf8'), b(cur.fetchone()[0]))
        self.assertQuotedEqual(f"SELECT '{snowman}';".encode('utf8'),
            cur.mogrify(f"SELECT '{snowman}';"))

        # unicode args
        cur.execute("SELECT %s;", (snowman,))
        self.assertEqual(snowman.encode("utf-8"), b(cur.fetchone()[0]))
        self.assertQuotedEqual(f"SELECT '{snowman}';".encode('utf8'),
            cur.mogrify("SELECT %s;", (snowman,)))

        # unicode query and args
        cur.execute("SELECT %s;", (snowman,))
        self.assertEqual(snowman.encode("utf-8"), b(cur.fetchone()[0]))
        self.assertQuotedEqual(f"SELECT '{snowman}';".encode('utf8'),
            cur.mogrify("SELECT %s;", (snowman,)))

    def test_mogrify_decimal_explodes(self):
        conn = self.conn
        cur = conn.cursor()
        self.assertEqual(b'SELECT 10.3;',
            cur.mogrify("SELECT %s;", (Decimal("10.3"),)))

    @skip_if_no_getrefcount
    def test_mogrify_leak_on_multiple_reference(self):
        # issue #81: reference leak when a parameter value is referenced
        # more than once from a dict.
        cur = self.conn.cursor()
        foo = (lambda x: x)('foo') * 10
        nref1 = sys.getrefcount(foo)
        cur.mogrify("select %(foo)s, %(foo)s, %(foo)s", {'foo': foo})
        nref2 = sys.getrefcount(foo)
        self.assertEqual(nref1, nref2)

    def test_modify_closed(self):
        cur = self.conn.cursor()
        cur.close()
        sql = cur.mogrify("select %s", (10,))
        self.assertEqual(sql, b"select 10")

    def test_bad_placeholder(self):
        cur = self.conn.cursor()
        self.assertRaises(psycopg2.ProgrammingError,
            cur.mogrify, "select %(foo", {})
        self.assertRaises(psycopg2.ProgrammingError,
            cur.mogrify, "select %(foo", {'foo': 1})
        self.assertRaises(psycopg2.ProgrammingError,
            cur.mogrify, "select %(foo, %(bar)", {'foo': 1})
        self.assertRaises(psycopg2.ProgrammingError,
            cur.mogrify, "select %(foo, %(bar)", {'foo': 1, 'bar': 2})

    def test_cast(self):
        curs = self.conn.cursor()

        self.assertEqual(42, curs.cast(20, '42'))
        self.assertAlmostEqual(3.14, curs.cast(700, '3.14'))

        self.assertEqual(Decimal('123.45'), curs.cast(1700, '123.45'))

        self.assertEqual(date(2011, 1, 2), curs.cast(1082, '2011-01-02'))
        self.assertEqual("who am i?", curs.cast(705, 'who am i?'))  # unknown

    def test_cast_specificity(self):
        curs = self.conn.cursor()
        self.assertEqual("foo", curs.cast(705, 'foo'))

        D = psycopg2.extensions.new_type((705,), "DOUBLING", lambda v, c: v * 2)
        psycopg2.extensions.register_type(D, self.conn)
        self.assertEqual("foofoo", curs.cast(705, 'foo'))

        T = psycopg2.extensions.new_type((705,), "TREBLING", lambda v, c: v * 3)
        psycopg2.extensions.register_type(T, curs)
        self.assertEqual("foofoofoo", curs.cast(705, 'foo'))

        curs2 = self.conn.cursor()
        self.assertEqual("foofoo", curs2.cast(705, 'foo'))

    def test_weakref(self):
        curs = self.conn.cursor()
        w = ref(curs)
        del curs
        gc.collect()
        self.assert_(w() is None)

    def test_null_name(self):
        curs = self.conn.cursor(None)
        self.assertEqual(curs.name, None)

    def test_description_attribs(self):
        curs = self.conn.cursor()
        curs.execute("""select
            3.14::decimal(10,2) as pi,
            'hello'::text as hi,
            '2010-02-18'::date as now;
            """)
        self.assertEqual(len(curs.description), 3)
        for c in curs.description:
            self.assertEqual(len(c), 7)  # DBAPI happy
            for a in ('name', 'type_code', 'display_size', 'internal_size',
                    'precision', 'scale', 'null_ok'):
                self.assert_(hasattr(c, a), a)

        c = curs.description[0]
        self.assertEqual(c.name, 'pi')
        self.assert_(c.type_code in psycopg2.extensions.DECIMAL.values)
        if crdb_version(self.conn) is None:
            self.assert_(c.internal_size > 0)
            self.assertEqual(c.precision, 10)
            self.assertEqual(c.scale, 2)

        c = curs.description[1]
        self.assertEqual(c.name, 'hi')
        self.assert_(c.type_code in psycopg2.STRING.values)
        self.assert_(c.internal_size < 0)
        self.assertEqual(c.precision, None)
        self.assertEqual(c.scale, None)

        c = curs.description[2]
        self.assertEqual(c.name, 'now')
        self.assert_(c.type_code in psycopg2.extensions.DATE.values)
        self.assert_(c.internal_size > 0)
        self.assertEqual(c.precision, None)
        self.assertEqual(c.scale, None)

    @skip_if_crdb("table oid")
    def test_description_extra_attribs(self):
        curs = self.conn.cursor()
        curs.execute("""
            create table testcol (
                pi decimal(10,2),
                hi text)
            """)
        curs.execute("select oid from pg_class where relname = %s", ('testcol',))
        oid = curs.fetchone()[0]

        curs.execute("insert into testcol values (3.14, 'hello')")
        curs.execute("select hi, pi, 42 from testcol")
        self.assertEqual(curs.description[0].table_oid, oid)
        self.assertEqual(curs.description[0].table_column, 2)

        self.assertEqual(curs.description[1].table_oid, oid)
        self.assertEqual(curs.description[1].table_column, 1)

        self.assertEqual(curs.description[2].table_oid, None)
        self.assertEqual(curs.description[2].table_column, None)

    def test_description_slice(self):
        curs = self.conn.cursor()
        curs.execute("select 1::int4 as a")
        self.assertEqual(curs.description[0][0:2], ('a', 23))

    def test_pickle_description(self):
        curs = self.conn.cursor()
        curs.execute('SELECT 1 AS foo')
        description = curs.description

        pickled = pickle.dumps(description, pickle.HIGHEST_PROTOCOL)
        unpickled = pickle.loads(pickled)

        self.assertEqual(description, unpickled)

    def test_column_refcount(self):
        # Reproduce crash describe in ticket #1252
        from psycopg2.extensions import Column

        def do_stuff():
            _ = Column(name='my_column')

        for _ in range(1000):
            do_stuff()

    def test_bad_subclass(self):
        # check that we get an error message instead of a segfault
        # for badly written subclasses.
        # see https://stackoverflow.com/questions/22019341/
        class StupidCursor(psycopg2.extensions.cursor):
            def __init__(self, *args, **kwargs):
                # I am stupid so not calling superclass init
                pass

        cur = StupidCursor()
        self.assertRaises(psycopg2.InterfaceError, cur.execute, 'select 1')
        self.assertRaises(psycopg2.InterfaceError, cur.executemany,
            'select 1', [])

    def test_callproc_badparam(self):
        cur = self.conn.cursor()
        self.assertRaises(TypeError, cur.callproc, 'lower', 42)

    # It would be inappropriate to test callproc's named parameters in the
    # DBAPI2.0 test section because they are a psycopg2 extension.
    @skip_before_postgres(9, 0)
    @skip_if_crdb("stored procedure")
    def test_callproc_dict(self):
        # This parameter name tests for injection and quote escaping
        paramname = '''
            Robert'); drop table "students" --
        '''.strip()
        escaped_paramname = '"%s"' % paramname.replace('"', '""')
        procname = 'pg_temp.randall'

        cur = self.conn.cursor()

        # Set up the temporary function
        cur.execute(f'''
            CREATE FUNCTION {procname}({escaped_paramname} INT)
            RETURNS INT AS
                'SELECT $1 * $1'
            LANGUAGE SQL
        ''')

        # Make sure callproc works right
        cur.callproc(procname, {paramname: 2})
        self.assertEquals(cur.fetchone()[0], 4)

        # Make sure callproc fails right
        failing_cases = [
            ({paramname: 2, 'foo': 'bar'}, psycopg2.ProgrammingError),
            ({paramname: '2'}, psycopg2.ProgrammingError),
            ({paramname: 'two'}, psycopg2.ProgrammingError),
            ({'bj\xc3rn': 2}, psycopg2.ProgrammingError),
            ({3: 2}, TypeError),
            ({self: 2}, TypeError),
        ]
        for parameter_sequence, exception in failing_cases:
            self.assertRaises(exception, cur.callproc, procname, parameter_sequence)
            self.conn.rollback()

    @skip_if_no_superuser
    @skip_if_windows
    @skip_if_crdb("backend pid")
    @skip_before_postgres(8, 4)
    def test_external_close_sync(self):
        # If a "victim" connection is closed by a "control" connection
        # behind psycopg2's back, psycopg2 always handles it correctly:
        # raise OperationalError, set conn.closed to 2. This reproduces
        # issue #443, a race between control_conn closing victim_conn and
        # psycopg2 noticing.
        control_conn = self.conn
        connect_func = self.connect

        def wait_func(conn):
            pass

        self._test_external_close(control_conn, connect_func, wait_func)

    @skip_if_no_superuser
    @skip_if_windows
    @skip_if_crdb("backend pid")
    @skip_before_postgres(8, 4)
    def test_external_close_async(self):
        # Issue #443 is in the async code too. Since the fix is duplicated,
        # so is the test.
        control_conn = self.conn

        def connect_func():
            return self.connect(async_=True)

        wait_func = psycopg2.extras.wait_select
        self._test_external_close(control_conn, connect_func, wait_func)

    def _test_external_close(self, control_conn, connect_func, wait_func):
        # The short sleep before using victim_conn the second time makes it
        # much more likely to lose the race and see the bug. Repeating the
        # test several times makes it even more likely.
        for i in range(10):
            victim_conn = connect_func()
            wait_func(victim_conn)

            with victim_conn.cursor() as cur:
                cur.execute('select pg_backend_pid()')
                wait_func(victim_conn)
                pid1 = cur.fetchall()[0][0]

            with control_conn.cursor() as cur:
                cur.execute('select pg_terminate_backend(%s)', (pid1,))

            time.sleep(0.001)

            def f():
                with victim_conn.cursor() as cur:
                    cur.execute('select 1')
                    wait_func(victim_conn)

            self.assertRaises(psycopg2.OperationalError, f)

            self.assertEqual(victim_conn.closed, 2)

    @skip_before_postgres(8, 2)
    def test_rowcount_on_executemany_returning(self):
        cur = self.conn.cursor()
        cur.execute("create table execmany(id serial primary key, data int)")
        cur.executemany(
            "insert into execmany (data) values (%s)",
            [(i,) for i in range(4)])
        self.assertEqual(cur.rowcount, 4)

        cur.executemany(
            "insert into execmany (data) values (%s) returning data",
            [(i,) for i in range(5)])
        self.assertEqual(cur.rowcount, 5)

    @skip_before_postgres(9)
    def test_pgresult_ptr(self):
        curs = self.conn.cursor()
        self.assert_(curs.pgresult_ptr is None)

        curs.execute("select 'x'")
        self.assert_(curs.pgresult_ptr is not None)

        try:
            f = self.libpq.PQcmdStatus
        except AttributeError:
            pass
        else:
            f.argtypes = [ctypes.c_void_p]
            f.restype = ctypes.c_char_p
            status = f(curs.pgresult_ptr)
            self.assertEqual(status, b'SELECT 1')

        curs.close()
        self.assert_(curs.pgresult_ptr is None)


@skip_if_crdb("named cursor")
class NamedCursorTests(ConnectingTestCase):
    def test_invalid_name(self):
        curs = self.conn.cursor()
        curs.execute("create table invname (data int);")
        for i in (10, 20, 30):
            curs.execute("insert into invname values (%s)", (i,))
        curs.close()

        curs = self.conn.cursor(r'1-2-3 \ "test"')
        curs.execute("select data from invname order by data")
        self.assertEqual(curs.fetchall(), [(10,), (20,), (30,)])

    def _create_withhold_table(self):
        curs = self.conn.cursor()
        try:
            curs.execute("drop table withhold")
        except psycopg2.ProgrammingError:
            self.conn.rollback()
        curs.execute("create table withhold (data int)")
        for i in (10, 20, 30):
            curs.execute("insert into withhold values (%s)", (i,))
        curs.close()

    def test_withhold(self):
        self.assertRaises(psycopg2.ProgrammingError, self.conn.cursor,
                          withhold=True)

        self._create_withhold_table()
        curs = self.conn.cursor("W")
        self.assertEqual(curs.withhold, False)
        curs.withhold = True
        self.assertEqual(curs.withhold, True)
        curs.execute("select data from withhold order by data")
        self.conn.commit()
        self.assertEqual(curs.fetchall(), [(10,), (20,), (30,)])
        curs.close()

        curs = self.conn.cursor("W", withhold=True)
        self.assertEqual(curs.withhold, True)
        curs.execute("select data from withhold order by data")
        self.conn.commit()
        self.assertEqual(curs.fetchall(), [(10,), (20,), (30,)])

        curs = self.conn.cursor()
        curs.execute("drop table withhold")
        self.conn.commit()

    def test_withhold_no_begin(self):
        self._create_withhold_table()
        curs = self.conn.cursor("w", withhold=True)
        curs.execute("select data from withhold order by data")
        self.assertEqual(curs.fetchone(), (10,))
        self.assertEqual(self.conn.status, psycopg2.extensions.STATUS_BEGIN)
        self.assertEqual(self.conn.info.transaction_status,
                         psycopg2.extensions.TRANSACTION_STATUS_INTRANS)

        self.conn.commit()
        self.assertEqual(self.conn.status, psycopg2.extensions.STATUS_READY)
        self.assertEqual(self.conn.info.transaction_status,
                         psycopg2.extensions.TRANSACTION_STATUS_IDLE)

        self.assertEqual(curs.fetchone(), (20,))
        self.assertEqual(self.conn.status, psycopg2.extensions.STATUS_READY)
        self.assertEqual(self.conn.info.transaction_status,
                         psycopg2.extensions.TRANSACTION_STATUS_IDLE)

        curs.close()
        self.assertEqual(self.conn.status, psycopg2.extensions.STATUS_READY)
        self.assertEqual(self.conn.info.transaction_status,
                         psycopg2.extensions.TRANSACTION_STATUS_IDLE)

    def test_withhold_autocommit(self):
        self._create_withhold_table()
        self.conn.commit()
        self.conn.autocommit = True
        curs = self.conn.cursor("w", withhold=True)
        curs.execute("select data from withhold order by data")

        self.assertEqual(curs.fetchone(), (10,))
        self.assertEqual(self.conn.status, psycopg2.extensions.STATUS_READY)
        self.assertEqual(self.conn.info.transaction_status,
                         psycopg2.extensions.TRANSACTION_STATUS_IDLE)

        self.conn.commit()
        self.assertEqual(self.conn.status, psycopg2.extensions.STATUS_READY)
        self.assertEqual(self.conn.info.transaction_status,
                         psycopg2.extensions.TRANSACTION_STATUS_IDLE)

        curs.close()
        self.assertEqual(self.conn.status, psycopg2.extensions.STATUS_READY)
        self.assertEqual(self.conn.info.transaction_status,
                         psycopg2.extensions.TRANSACTION_STATUS_IDLE)

    def test_scrollable(self):
        self.assertRaises(psycopg2.ProgrammingError, self.conn.cursor,
                          scrollable=True)

        curs = self.conn.cursor()
        curs.execute("create table scrollable (data int)")
        curs.executemany("insert into scrollable values (%s)",
            [(i,) for i in range(100)])
        curs.close()

        for t in range(2):
            if not t:
                curs = self.conn.cursor("S")
                self.assertEqual(curs.scrollable, None)
                curs.scrollable = True
            else:
                curs = self.conn.cursor("S", scrollable=True)

            self.assertEqual(curs.scrollable, True)
            curs.itersize = 10

            # complex enough to make postgres cursors declare without
            # scroll/no scroll to fail
            curs.execute("""
                select x.data
                from scrollable x
                join scrollable y on x.data = y.data
                order by y.data""")
            for i, (n,) in enumerate(curs):
                self.assertEqual(i, n)

            curs.scroll(-1)
            for i in range(99, -1, -1):
                curs.scroll(-1)
                self.assertEqual(i, curs.fetchone()[0])
                curs.scroll(-1)

            curs.close()

    def test_not_scrollable(self):
        self.assertRaises(psycopg2.ProgrammingError, self.conn.cursor,
                          scrollable=False)

        curs = self.conn.cursor()
        curs.execute("create table scrollable (data int)")
        curs.executemany("insert into scrollable values (%s)",
            [(i,) for i in range(100)])
        curs.close()

        curs = self.conn.cursor("S")    # default scrollability
        curs.execute("select * from scrollable")
        self.assertEqual(curs.scrollable, None)
        curs.scroll(2)
        try:
            curs.scroll(-1)
        except psycopg2.OperationalError:
            return self.skipTest("can't evaluate non-scrollable cursor")
        curs.close()

        curs = self.conn.cursor("S", scrollable=False)
        self.assertEqual(curs.scrollable, False)
        curs.execute("select * from scrollable")
        curs.scroll(2)
        self.assertRaises(psycopg2.OperationalError, curs.scroll, -1)

    @slow
    @skip_before_postgres(8, 2)
    def test_iter_named_cursor_efficient(self):
        curs = self.conn.cursor('tmp')
        # if these records are fetched in the same roundtrip their
        # timestamp will not be influenced by the pause in Python world.
        curs.execute("""select clock_timestamp() from generate_series(1,2)""")
        i = iter(curs)
        t1 = next(i)[0]
        time.sleep(0.2)
        t2 = next(i)[0]
        self.assert_((t2 - t1).microseconds * 1e-6 < 0.1,
            f"named cursor records fetched in 2 roundtrips (delta: {t2 - t1})")

    @skip_before_postgres(8, 0)
    def test_iter_named_cursor_default_itersize(self):
        curs = self.conn.cursor('tmp')
        curs.execute('select generate_series(1,50)')
        rv = [(r[0], curs.rownumber) for r in curs]
        # everything swallowed in one gulp
        self.assertEqual(rv, [(i, i) for i in range(1, 51)])

    @skip_before_postgres(8, 0)
    def test_iter_named_cursor_itersize(self):
        curs = self.conn.cursor('tmp')
        curs.itersize = 30
        curs.execute('select generate_series(1,50)')
        rv = [(r[0], curs.rownumber) for r in curs]
        # everything swallowed in two gulps
        self.assertEqual(rv, [(i, ((i - 1) % 30) + 1) for i in range(1, 51)])

    @skip_before_postgres(8, 0)
    def test_iter_named_cursor_rownumber(self):
        curs = self.conn.cursor('tmp')
        # note: this fails if itersize < dataset: internally we check
        # rownumber == rowcount to detect when to read anoter page, so we
        # would need an extra attribute to have a monotonic rownumber.
        curs.itersize = 20
        curs.execute('select generate_series(1,10)')
        for i, rec in enumerate(curs):
            self.assertEqual(i + 1, curs.rownumber)

    @skip_before_postgres(8, 0)
    def test_named_cursor_stealing(self):
        # you can use a named cursor to iterate on a refcursor created
        # somewhere else
        cur1 = self.conn.cursor()
        cur1.execute("DECLARE test CURSOR WITHOUT HOLD "
            " FOR SELECT generate_series(1,7)")

        cur2 = self.conn.cursor('test')
        # can call fetch without execute
        self.assertEqual((1,), cur2.fetchone())
        self.assertEqual([(2,), (3,), (4,)], cur2.fetchmany(3))
        self.assertEqual([(5,), (6,), (7,)], cur2.fetchall())

    @skip_before_postgres(8, 2)
    def test_named_noop_close(self):
        cur = self.conn.cursor('test')
        cur.close()

    @skip_before_postgres(8, 2)
    def test_stolen_named_cursor_close(self):
        cur1 = self.conn.cursor()
        cur1.execute("DECLARE test CURSOR WITHOUT HOLD "
            " FOR SELECT generate_series(1,7)")
        cur2 = self.conn.cursor('test')
        cur2.close()

        cur1.execute("DECLARE test CURSOR WITHOUT HOLD "
            " FOR SELECT generate_series(1,7)")
        cur2 = self.conn.cursor('test')
        cur2.close()

    @skip_before_postgres(8, 0)
    def test_scroll(self):
        cur = self.conn.cursor()
        cur.execute("select generate_series(0,9)")
        cur.scroll(2)
        self.assertEqual(cur.fetchone(), (2,))
        cur.scroll(2)
        self.assertEqual(cur.fetchone(), (5,))
        cur.scroll(2, mode='relative')
        self.assertEqual(cur.fetchone(), (8,))
        cur.scroll(-1)
        self.assertEqual(cur.fetchone(), (8,))
        cur.scroll(-2)
        self.assertEqual(cur.fetchone(), (7,))
        cur.scroll(2, mode='absolute')
        self.assertEqual(cur.fetchone(), (2,))

        # on the boundary
        cur.scroll(0, mode='absolute')
        self.assertEqual(cur.fetchone(), (0,))
        self.assertRaises((IndexError, psycopg2.ProgrammingError),
            cur.scroll, -1, mode='absolute')
        cur.scroll(0, mode='absolute')
        self.assertRaises((IndexError, psycopg2.ProgrammingError),
            cur.scroll, -1)

        cur.scroll(9, mode='absolute')
        self.assertEqual(cur.fetchone(), (9,))
        self.assertRaises((IndexError, psycopg2.ProgrammingError),
            cur.scroll, 10, mode='absolute')
        cur.scroll(9, mode='absolute')
        self.assertRaises((IndexError, psycopg2.ProgrammingError),
            cur.scroll, 1)

    @skip_before_postgres(8, 0)
    def test_scroll_named(self):
        cur = self.conn.cursor('tmp', scrollable=True)
        cur.execute("select generate_series(0,9)")
        cur.scroll(2)
        self.assertEqual(cur.fetchone(), (2,))
        cur.scroll(2)
        self.assertEqual(cur.fetchone(), (5,))
        cur.scroll(2, mode='relative')
        self.assertEqual(cur.fetchone(), (8,))
        cur.scroll(9, mode='absolute')
        self.assertEqual(cur.fetchone(), (9,))


def test_suite():
    return unittest.TestLoader().loadTestsFromName(__name__)


if __name__ == "__main__":
    unittest.main()