/brz/remove-bazaar

# Copyright (C) 2005, 2006, 2007 Canonical Ltd

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; either version 2 of the License, or

# (at your option) any later version.

#

# This program 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 General Public License for more details.

#

# You should have received a copy of the GNU General Public License

# along with this program; if not, write to the Free Software

# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

"""Tests for the test framework."""

import cStringIO

import os

from StringIO import StringIO

import sys

import time

import unittest

import warnings

import bzrlib

from bzrlib import (

    bzrdir,

    errors,

    memorytree,

    osutils,

    repository,

    symbol_versioning,

    tests,

    )

from bzrlib.progress import _BaseProgressBar

from bzrlib.repofmt import weaverepo

from bzrlib.symbol_versioning import (

    one_zero,

    zero_eleven,

    zero_ten,

    )

from bzrlib.tests import (

                          ChrootedTestCase,

                          ExtendedTestResult,

                          Feature,

                          KnownFailure,

                          TestCase,

                          TestCaseInTempDir,

                          TestCaseWithMemoryTransport,

                          TestCaseWithTransport,

                          TestNotApplicable,

                          TestSkipped,

                          TestSuite,

                          TestUtil,

                          TextTestRunner,

                          UnavailableFeature,

                          condition_id_re,

                          condition_isinstance,

                          exclude_tests_by_condition,

                          exclude_tests_by_re,

                          filter_suite_by_condition,

                          filter_suite_by_re,

                          iter_suite_tests,

                          preserve_input,

                          randomize_suite,

                          sort_suite_by_re,

                          split_suite_by_re,

                          test_lsprof,

                          test_suite,

                          )

from bzrlib.tests.test_sftp_transport import TestCaseWithSFTPServer

from bzrlib.tests.TestUtil import _load_module_by_name

from bzrlib.trace import note

from bzrlib.transport.memory import MemoryServer, MemoryTransport

from bzrlib.version import _get_bzr_source_tree

class SelftestTests(TestCase):

    def test_import_tests(self):

        mod = _load_module_by_name('bzrlib.tests.test_selftest')

        self.assertEqual(mod.SelftestTests, SelftestTests)

    def test_import_test_failure(self):

        self.assertRaises(ImportError,

                          _load_module_by_name,

                          'bzrlib.no-name-yet')

class MetaTestLog(TestCase):

    def test_logging(self):

        """Test logs are captured when a test fails."""

        self.log('a test message')

        self._log_file.flush()

        self.assertContainsRe(self._get_log(keep_log_file=True),

                              'a test message\n')

class TestTreeShape(TestCaseInTempDir):

    def test_unicode_paths(self):

        filename = u'hell\u00d8'

        try:

            self.build_tree_contents([(filename, 'contents of hello')])

        except UnicodeEncodeError:

            raise TestSkipped("can't build unicode working tree in "

                "filesystem encoding %s" % sys.getfilesystemencoding())

        self.failUnlessExists(filename)

class TestTransportProviderAdapter(TestCase):

    """A group of tests that test the transport implementation adaption core.

    This is a meta test that the tests are applied to all available 

    transports.

    This will be generalised in the future which is why it is in this 

    test file even though it is specific to transport tests at the moment.

    """

    def test_get_transport_permutations(self):

        # this checks that we the module get_test_permutations call

        # is made by the adapter get_transport_test_permitations method.

        class MockModule(object):

            def get_test_permutations(self):

                return sample_permutation

        sample_permutation = [(1,2), (3,4)]

        from bzrlib.tests.test_transport_implementations \

            import TransportTestProviderAdapter

        adapter = TransportTestProviderAdapter()

        self.assertEqual(sample_permutation,

                         adapter.get_transport_test_permutations(MockModule()))

    def test_adapter_checks_all_modules(self):

        # this checks that the adapter returns as many permurtations as

        # there are in all the registered# transport modules for there

        # - we assume if this matches its probably doing the right thing

        # especially in combination with the tests for setting the right

        # classes below.

        from bzrlib.tests.test_transport_implementations \

            import TransportTestProviderAdapter

        from bzrlib.transport import _get_transport_modules

        modules = _get_transport_modules()

        permutation_count = 0

        for module in modules:

            try:

                permutation_count += len(reduce(getattr, 

                    (module + ".get_test_permutations").split('.')[1:],

                     __import__(module))())

            except errors.DependencyNotPresent:

                pass

        input_test = TestTransportProviderAdapter(

            "test_adapter_sets_transport_class")

        adapter = TransportTestProviderAdapter()

        self.assertEqual(permutation_count,

                         len(list(iter(adapter.adapt(input_test)))))

    def test_adapter_sets_transport_class(self):

        # Check that the test adapter inserts a transport and server into the

        # generated test.

        #

        # This test used to know about all the possible transports and the

        # order they were returned but that seems overly brittle (mbp

        # 20060307)

        from bzrlib.tests.test_transport_implementations \

            import TransportTestProviderAdapter

        scenarios = TransportTestProviderAdapter().scenarios

        # there are at least that many builtin transports

        self.assertTrue(len(scenarios) > 6)

        one_scenario = scenarios[0]

        self.assertIsInstance(one_scenario[0], str)

        self.assertTrue(issubclass(one_scenario[1]["transport_class"],

                                   bzrlib.transport.Transport))

        self.assertTrue(issubclass(one_scenario[1]["transport_server"],

                                   bzrlib.transport.Server))

class TestBranchProviderAdapter(TestCase):

    """A group of tests that test the branch implementation test adapter."""

    def test_constructor(self):

        # check that constructor parameters are passed through to the adapted

        # test.

        from bzrlib.tests.branch_implementations import BranchTestProviderAdapter

        server1 = "a"

        server2 = "b"

        formats = [("c", "C"), ("d", "D")]

        adapter = BranchTestProviderAdapter(server1, server2, formats)

        self.assertEqual(2, len(adapter.scenarios))

        self.assertEqual([

            ('str',

             {'branch_format': 'c',

              'bzrdir_format': 'C',

              'transport_readonly_server': 'b',

              'transport_server': 'a'}),

            ('str',

             {'branch_format': 'd',

              'bzrdir_format': 'D',

              'transport_readonly_server': 'b',

              'transport_server': 'a'})],

            adapter.scenarios)

class TestBzrDirProviderAdapter(TestCase):

    """A group of tests that test the bzr dir implementation test adapter."""

    def test_adapted_tests(self):

        # check that constructor parameters are passed through to the adapted

        # test.

        from bzrlib.tests.bzrdir_implementations import BzrDirTestProviderAdapter

        vfs_factory = "v"

        server1 = "a"

        server2 = "b"

        formats = ["c", "d"]

        adapter = BzrDirTestProviderAdapter(vfs_factory,

            server1, server2, formats)

        self.assertEqual([

            ('str',

             {'bzrdir_format': 'c',

              'transport_readonly_server': 'b',

              'transport_server': 'a',

              'vfs_transport_factory': 'v'}),

            ('str',

             {'bzrdir_format': 'd',

              'transport_readonly_server': 'b',

              'transport_server': 'a',

              'vfs_transport_factory': 'v'})],

            adapter.scenarios)

class TestRepositoryProviderAdapter(TestCase):

    """A group of tests that test the repository implementation test adapter."""

    def test_constructor(self):

        # check that constructor parameters are passed through to the

        # scenarios.

        from bzrlib.tests.repository_implementations import RepositoryTestProviderAdapter

        server1 = "a"

        server2 = "b"

        formats = [("c", "C"), ("d", "D")]

        adapter = RepositoryTestProviderAdapter(server1, server2, formats)

        self.assertEqual([

            ('str',

             {'bzrdir_format': 'C',

              'repository_format': 'c',

              'transport_readonly_server': 'b',

              'transport_server': 'a'}),

            ('str',

             {'bzrdir_format': 'D',

              'repository_format': 'd',

              'transport_readonly_server': 'b',

              'transport_server': 'a'})],

            adapter.scenarios)

    def test_setting_vfs_transport(self):

        """The vfs_transport_factory can be set optionally."""

        from bzrlib.tests.repository_implementations import RepositoryTestProviderAdapter

        formats = [("a", "b"), ("c", "d")]

        adapter = RepositoryTestProviderAdapter(None, None, formats,

            vfs_transport_factory="vfs")

        self.assertEqual([

            ('str',

             {'bzrdir_format': 'b',

              'repository_format': 'a',

              'transport_readonly_server': None,

              'transport_server': None,

              'vfs_transport_factory': 'vfs'}),

            ('str',

             {'bzrdir_format': 'd',

              'repository_format': 'c',

              'transport_readonly_server': None,

              'transport_server': None,

              'vfs_transport_factory': 'vfs'})],

            adapter.scenarios)

    def test_formats_to_scenarios(self):

        """The adapter can generate all the scenarios needed."""

        from bzrlib.tests.repository_implementations import RepositoryTestProviderAdapter

        no_vfs_adapter = RepositoryTestProviderAdapter("server", "readonly",

            [], None)

        vfs_adapter = RepositoryTestProviderAdapter("server", "readonly",

            [], vfs_transport_factory="vfs")

        # no_vfs generate scenarios without vfs_transport_factor

        formats = [("c", "C"), (1, "D")]

        self.assertEqual([

            ('str',

             {'bzrdir_format': 'C',

              'repository_format': 'c',

              'transport_readonly_server': 'readonly',

              'transport_server': 'server'}),

            ('int',

             {'bzrdir_format': 'D',

              'repository_format': 1,

              'transport_readonly_server': 'readonly',

              'transport_server': 'server'})],

            no_vfs_adapter.formats_to_scenarios(formats))

        self.assertEqual([

            ('str',

             {'bzrdir_format': 'C',

              'repository_format': 'c',

              'transport_readonly_server': 'readonly',

              'transport_server': 'server',

              'vfs_transport_factory': 'vfs'}),

            ('int',

             {'bzrdir_format': 'D',

              'repository_format': 1,

              'transport_readonly_server': 'readonly',

              'transport_server': 'server',

              'vfs_transport_factory': 'vfs'})],

            vfs_adapter.formats_to_scenarios(formats))

class TestTestScenarioApplier(TestCase):

    """Tests for the test adaption facilities."""

    def test_adapt_applies_scenarios(self):

        from bzrlib.tests.repository_implementations import TestScenarioApplier

        input_test = TestTestScenarioApplier("test_adapt_test_to_scenario")

        adapter = TestScenarioApplier()

        adapter.scenarios = [("1", "dict"), ("2", "settings")]

        calls = []

        def capture_call(test, scenario):

            calls.append((test, scenario))

            return test

        adapter.adapt_test_to_scenario = capture_call

        adapter.adapt(input_test)

        self.assertEqual([(input_test, ("1", "dict")),

            (input_test, ("2", "settings"))], calls)

    def test_adapt_test_to_scenario(self):

        from bzrlib.tests.repository_implementations import TestScenarioApplier

        input_test = TestTestScenarioApplier("test_adapt_test_to_scenario")

        adapter = TestScenarioApplier()

        # setup two adapted tests

        adapted_test1 = adapter.adapt_test_to_scenario(input_test,

            ("new id",

            {"bzrdir_format":"bzr_format",

             "repository_format":"repo_fmt",

             "transport_server":"transport_server",

             "transport_readonly_server":"readonly-server"}))

        adapted_test2 = adapter.adapt_test_to_scenario(input_test,

            ("new id 2", {"bzrdir_format":None}))

        # input_test should have been altered.

        self.assertRaises(AttributeError, getattr, input_test, "bzrdir_format")

        # the new tests are mutually incompatible, ensuring it has 

        # made new ones, and unspecified elements in the scenario

        # should not have been altered.

        self.assertEqual("bzr_format", adapted_test1.bzrdir_format)

        self.assertEqual("repo_fmt", adapted_test1.repository_format)

        self.assertEqual("transport_server", adapted_test1.transport_server)

        self.assertEqual("readonly-server",

            adapted_test1.transport_readonly_server)

        self.assertEqual(

            "bzrlib.tests.test_selftest.TestTestScenarioApplier."

            "test_adapt_test_to_scenario(new id)",

            adapted_test1.id())

        self.assertEqual(None, adapted_test2.bzrdir_format)

        self.assertEqual(

            "bzrlib.tests.test_selftest.TestTestScenarioApplier."

            "test_adapt_test_to_scenario(new id 2)",

            adapted_test2.id())

class TestInterRepositoryProviderAdapter(TestCase):

    """A group of tests that test the InterRepository test adapter."""

    def test_adapted_tests(self):

        # check that constructor parameters are passed through to the adapted

        # test.

        from bzrlib.tests.interrepository_implementations import \

            InterRepositoryTestProviderAdapter

        server1 = "a"

        server2 = "b"

        formats = [(str, "C1", "C2"), (int, "D1", "D2")]

        adapter = InterRepositoryTestProviderAdapter(server1, server2, formats)

        self.assertEqual([

            ('str',

             {'interrepo_class': str,

              'repository_format': 'C1',

              'repository_format_to': 'C2',

              'transport_readonly_server': 'b',

              'transport_server': 'a'}),

            ('int',

             {'interrepo_class': int,

              'repository_format': 'D1',

              'repository_format_to': 'D2',

              'transport_readonly_server': 'b',

              'transport_server': 'a'})],

            adapter.formats_to_scenarios(formats))

class TestInterVersionedFileProviderAdapter(TestCase):

    """A group of tests that test the InterVersionedFile test adapter."""

    def test_scenarios(self):

        # check that constructor parameters are passed through to the adapted

        # test.

        from bzrlib.tests.interversionedfile_implementations \

            import InterVersionedFileTestProviderAdapter

        server1 = "a"

        server2 = "b"

        formats = [(str, "C1", "C2"), (int, "D1", "D2")]

        adapter = InterVersionedFileTestProviderAdapter(server1, server2, formats)

        self.assertEqual([

            ('str',

             {'interversionedfile_class':str,

              'transport_readonly_server': 'b',

              'transport_server': 'a',

              'versionedfile_factory': 'C1',

              'versionedfile_factory_to': 'C2'}),

            ('int',

             {'interversionedfile_class': int,

              'transport_readonly_server': 'b',

              'transport_server': 'a',

              'versionedfile_factory': 'D1',

              'versionedfile_factory_to': 'D2'})],

            adapter.scenarios)

class TestRevisionStoreProviderAdapter(TestCase):

    """A group of tests that test the RevisionStore test adapter."""

    def test_scenarios(self):

        # check that constructor parameters are passed through to the adapted

        # test.

        from bzrlib.tests.revisionstore_implementations \

            import RevisionStoreTestProviderAdapter

        # revision stores need a store factory - i.e. RevisionKnit

        #, a readonly and rw transport 

        # transport servers:

        server1 = "a"

        server2 = "b"

        store_factories = ["c", "d"]

        adapter = RevisionStoreTestProviderAdapter(server1, server2, store_factories)

        self.assertEqual([

            ('c',

             {'store_factory': 'c',

              'transport_readonly_server': 'b',

              'transport_server': 'a'}),

            ('d',

             {'store_factory': 'd',

              'transport_readonly_server': 'b',

              'transport_server': 'a'})],

            adapter.scenarios)

class TestWorkingTreeProviderAdapter(TestCase):

    """A group of tests that test the workingtree implementation test adapter."""

    def test_scenarios(self):

        # check that constructor parameters are passed through to the adapted

        # test.

        from bzrlib.tests.workingtree_implementations \

            import WorkingTreeTestProviderAdapter

        server1 = "a"

        server2 = "b"

        formats = [("c", "C"), ("d", "D")]

        adapter = WorkingTreeTestProviderAdapter(server1, server2, formats)

        self.assertEqual([

            ('str',

             {'bzrdir_format': 'C',

              'transport_readonly_server': 'b',

              'transport_server': 'a',

              'workingtree_format': 'c'}),

            ('str',

             {'bzrdir_format': 'D',

              'transport_readonly_server': 'b',

              'transport_server': 'a',

              'workingtree_format': 'd'})],

            adapter.scenarios)

class TestTreeProviderAdapter(TestCase):

    """Test the setup of tree_implementation tests."""

    def test_adapted_tests(self):

        # the tree implementation adapter is meant to setup one instance for

        # each working tree format, and one additional instance that will

        # use the default wt format, but create a revision tree for the tests.

        # this means that the wt ones should have the workingtree_to_test_tree

        # attribute set to 'return_parameter' and the revision one set to

        # revision_tree_from_workingtree.

        from bzrlib.tests.tree_implementations import (

            TreeTestProviderAdapter,

            return_parameter,

            revision_tree_from_workingtree

            )

        from bzrlib.workingtree import WorkingTreeFormat, WorkingTreeFormat3

        input_test = TestTreeProviderAdapter(

            "test_adapted_tests")

        server1 = "a"

        server2 = "b"

        formats = [("c", "C"), ("d", "D")]

        adapter = TreeTestProviderAdapter(server1, server2, formats)

        suite = adapter.adapt(input_test)

        tests = list(iter(suite))

        self.assertEqual(4, len(tests))

        # this must match the default format setp up in

        # TreeTestProviderAdapter.adapt

        default_format = WorkingTreeFormat3

        self.assertEqual(tests[0].workingtree_format, formats[0][0])

        self.assertEqual(tests[0].bzrdir_format, formats[0][1])

        self.assertEqual(tests[0].transport_server, server1)

        self.assertEqual(tests[0].transport_readonly_server, server2)

        self.assertEqual(tests[0].workingtree_to_test_tree, return_parameter)

        self.assertEqual(tests[1].workingtree_format, formats[1][0])

        self.assertEqual(tests[1].bzrdir_format, formats[1][1])

        self.assertEqual(tests[1].transport_server, server1)

        self.assertEqual(tests[1].transport_readonly_server, server2)

        self.assertEqual(tests[1].workingtree_to_test_tree, return_parameter)

        self.assertIsInstance(tests[2].workingtree_format, default_format)

        #self.assertEqual(tests[2].bzrdir_format,

        #                 default_format._matchingbzrdir)

        self.assertEqual(tests[2].transport_server, server1)

        self.assertEqual(tests[2].transport_readonly_server, server2)

        self.assertEqual(tests[2].workingtree_to_test_tree,

            revision_tree_from_workingtree)

class TestInterTreeProviderAdapter(TestCase):

    """A group of tests that test the InterTreeTestAdapter."""

    def test_adapted_tests(self):

        # check that constructor parameters are passed through to the adapted

        # test.

        # for InterTree tests we want the machinery to bring up two trees in

        # each instance: the base one, and the one we are interacting with.

        # because each optimiser can be direction specific, we need to test

        # each optimiser in its chosen direction.

        # unlike the TestProviderAdapter we dont want to automatically add a

        # parameterized one for WorkingTree - the optimisers will tell us what

        # ones to add.

        from bzrlib.tests.tree_implementations import (

            return_parameter,

            revision_tree_from_workingtree

            )

        from bzrlib.tests.intertree_implementations import (

            InterTreeTestProviderAdapter,

            )

        from bzrlib.workingtree import WorkingTreeFormat2, WorkingTreeFormat3

        input_test = TestInterTreeProviderAdapter(

            "test_adapted_tests")

        server1 = "a"

        server2 = "b"

        format1 = WorkingTreeFormat2()

        format2 = WorkingTreeFormat3()

        formats = [(str, format1, format2, "converter1"),

            (int, format2, format1, "converter2")]

        adapter = InterTreeTestProviderAdapter(server1, server2, formats)

        suite = adapter.adapt(input_test)

        tests = list(iter(suite))

        self.assertEqual(2, len(tests))

        self.assertEqual(tests[0].intertree_class, formats[0][0])

        self.assertEqual(tests[0].workingtree_format, formats[0][1])

        self.assertEqual(tests[0].workingtree_format_to, formats[0][2])

        self.assertEqual(tests[0].mutable_trees_to_test_trees, formats[0][3])

        self.assertEqual(tests[0].workingtree_to_test_tree, return_parameter)

        self.assertEqual(tests[0].transport_server, server1)

        self.assertEqual(tests[0].transport_readonly_server, server2)

        self.assertEqual(tests[1].intertree_class, formats[1][0])

        self.assertEqual(tests[1].workingtree_format, formats[1][1])

        self.assertEqual(tests[1].workingtree_format_to, formats[1][2])

        self.assertEqual(tests[1].mutable_trees_to_test_trees, formats[1][3])

        self.assertEqual(tests[1].workingtree_to_test_tree, return_parameter)

        self.assertEqual(tests[1].transport_server, server1)

        self.assertEqual(tests[1].transport_readonly_server, server2)

class TestTestCaseInTempDir(TestCaseInTempDir):

    def test_home_is_not_working(self):

        self.assertNotEqual(self.test_dir, self.test_home_dir)

        cwd = osutils.getcwd()

        self.assertIsSameRealPath(self.test_dir, cwd)

        self.assertIsSameRealPath(self.test_home_dir, os.environ['HOME'])

class TestTestCaseWithMemoryTransport(TestCaseWithMemoryTransport):

    def test_home_is_non_existant_dir_under_root(self):

        """The test_home_dir for TestCaseWithMemoryTransport is missing.

        This is because TestCaseWithMemoryTransport is for tests that do not

        need any disk resources: they should be hooked into bzrlib in such a 

        way that no global settings are being changed by the test (only a 

        few tests should need to do that), and having a missing dir as home is

        an effective way to ensure that this is the case.

        """

        self.assertIsSameRealPath(

            self.TEST_ROOT + "/MemoryTransportMissingHomeDir",

            self.test_home_dir)

        self.assertIsSameRealPath(self.test_home_dir, os.environ['HOME'])

    def test_cwd_is_TEST_ROOT(self):

        self.assertIsSameRealPath(self.test_dir, self.TEST_ROOT)

        cwd = osutils.getcwd()

        self.assertIsSameRealPath(self.test_dir, cwd)

    def test_make_branch_and_memory_tree(self):

        """In TestCaseWithMemoryTransport we should not make the branch on disk.

        This is hard to comprehensively robustly test, so we settle for making

        a branch and checking no directory was created at its relpath.

        """

        tree = self.make_branch_and_memory_tree('dir')

        # Guard against regression into MemoryTransport leaking

        # files to disk instead of keeping them in memory.

        self.failIf(osutils.lexists('dir'))

        self.assertIsInstance(tree, memorytree.MemoryTree)

    def test_make_branch_and_memory_tree_with_format(self):

        """make_branch_and_memory_tree should accept a format option."""

        format = bzrdir.BzrDirMetaFormat1()

        format.repository_format = weaverepo.RepositoryFormat7()

        tree = self.make_branch_and_memory_tree('dir', format=format)

        # Guard against regression into MemoryTransport leaking

        # files to disk instead of keeping them in memory.

        self.failIf(osutils.lexists('dir'))

        self.assertIsInstance(tree, memorytree.MemoryTree)

        self.assertEqual(format.repository_format.__class__,

            tree.branch.repository._format.__class__)

    def test_safety_net(self):

        """No test should modify the safety .bzr directory.

        We just test that the _check_safety_net private method raises

        AssertionError, it's easier than building a test suite with the same

        test.

        """

        # Oops, a commit in the current directory (i.e. without local .bzr

        # directory) will crawl up the hierarchy to find a .bzr directory.

        self.run_bzr(['commit', '-mfoo', '--unchanged'])

        # But we have a safety net in place.

        self.assertRaises(AssertionError, self._check_safety_net)

class TestTestCaseWithTransport(TestCaseWithTransport):

    """Tests for the convenience functions TestCaseWithTransport introduces."""

    def test_get_readonly_url_none(self):

        from bzrlib.transport import get_transport

        from bzrlib.transport.memory import MemoryServer

        from bzrlib.transport.readonly import ReadonlyTransportDecorator

        self.vfs_transport_factory = MemoryServer

        self.transport_readonly_server = None

        # calling get_readonly_transport() constructs a decorator on the url

        # for the server

        url = self.get_readonly_url()

        url2 = self.get_readonly_url('foo/bar')

        t = get_transport(url)

        t2 = get_transport(url2)

        self.failUnless(isinstance(t, ReadonlyTransportDecorator))

        self.failUnless(isinstance(t2, ReadonlyTransportDecorator))

        self.assertEqual(t2.base[:-1], t.abspath('foo/bar'))

    def test_get_readonly_url_http(self):

        from bzrlib.tests.http_server import HttpServer

        from bzrlib.transport import get_transport

        from bzrlib.transport.local import LocalURLServer

        from bzrlib.transport.http import HttpTransportBase

        self.transport_server = LocalURLServer

        self.transport_readonly_server = HttpServer

        # calling get_readonly_transport() gives us a HTTP server instance.

        url = self.get_readonly_url()

        url2 = self.get_readonly_url('foo/bar')

        # the transport returned may be any HttpTransportBase subclass

        t = get_transport(url)

        t2 = get_transport(url2)

        self.failUnless(isinstance(t, HttpTransportBase))

        self.failUnless(isinstance(t2, HttpTransportBase))

        self.assertEqual(t2.base[:-1], t.abspath('foo/bar'))