/brz/remove-bazaar

# Copyright (C) 2008 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 maps built on a CHK versionedfiles facility."""

from bzrlib.chk_map import (

    CHKMap,

    InternalNode,

    LeafNode,

    RootNode,

    ValueNode,

    _deserialise,

    )

from bzrlib.tests import TestCaseWithTransport

class TestCaseWithStore(TestCaseWithTransport):

    def get_chk_bytes(self):

        # The eassiest way to get a CHK store is a development3 repository and

        # then work with the chk_bytes attribute directly.

        repo = self.make_repository(".", format="development3")

        repo.lock_write()

        self.addCleanup(repo.unlock)

        repo.start_write_group()

        self.addCleanup(repo.abort_write_group)

        return repo.chk_bytes

    def _get_map(self, a_dict, maximum_size=0):

        chk_bytes = self.get_chk_bytes()

        root_key = CHKMap.from_dict(chk_bytes, a_dict, maximum_size=maximum_size)

        chkmap = CHKMap(chk_bytes, root_key)

        return chkmap

    def read_bytes(self, chk_bytes, key):

        stream = chk_bytes.get_record_stream([key], 'unordered', True)

        return stream.next().get_bytes_as("fulltext")

    def to_dict(self, node, *args):

        return dict(node.iteritems(*args))

class TestMap(TestCaseWithStore):

    def assertHasABMap(self, chk_bytes):

        root_key = ('sha1:29f1da33ce2323d754485fd308abc5ff17f3856e',)

        self.assertEqual(

            "chkroot:\n0\n1\na\x00sha1:cb29f32e561a1b7f862c38ccfd6bc7c7d892f04b\n",

            self.read_bytes(chk_bytes, root_key))

        self.assertEqual(

            "chkvalue:\nb",

            self.read_bytes(chk_bytes,

                ("sha1:cb29f32e561a1b7f862c38ccfd6bc7c7d892f04b",)))

    def assertHasEmptyMap(self, chk_bytes):

        root_key = ('sha1:d0826cf765ff45bd602f602ecb0efbe375ea3b50',)

        self.assertEqual("chkroot:\n0\n0\n", self.read_bytes(chk_bytes, root_key))

    def test_from_dict_empty(self):

        chk_bytes = self.get_chk_bytes()

        root_key = CHKMap.from_dict(chk_bytes, {})

        self.assertEqual(('sha1:d0826cf765ff45bd602f602ecb0efbe375ea3b50',),

            root_key)

        self.assertHasEmptyMap(chk_bytes)

    def test_from_dict_ab(self):

        chk_bytes = self.get_chk_bytes()

        root_key = CHKMap.from_dict(chk_bytes, {"a":"b"})

        self.assertEqual(('sha1:29f1da33ce2323d754485fd308abc5ff17f3856e',),

            root_key)

        self.assertHasABMap(chk_bytes)

    def test_apply_empty_ab(self):

        # applying a delta (None, "a", "b") to an empty chkmap generates the

        # same map as from_dict_ab.

        chk_bytes = self.get_chk_bytes()

        root_key = CHKMap.from_dict(chk_bytes, {})

        chkmap = CHKMap(chk_bytes, root_key)

        new_root = chkmap.apply_delta([(None, "a", "b")])

        self.assertEqual(('sha1:29f1da33ce2323d754485fd308abc5ff17f3856e',),

            new_root)

        self.assertHasABMap(chk_bytes)

        # The update should have left us with an in memory root node, with an

        # updated key.

        self.assertEqual(new_root, chkmap._root_node._key)

    def test_apply_ab_empty(self):

        # applying a delta ("a", None, None) to an empty chkmap generates the

        # same map as from_dict_ab.

        chk_bytes = self.get_chk_bytes()

        root_key = CHKMap.from_dict(chk_bytes, {"a":"b"})

        chkmap = CHKMap(chk_bytes, root_key)

        new_root = chkmap.apply_delta([("a", None, None)])

        self.assertEqual(('sha1:d0826cf765ff45bd602f602ecb0efbe375ea3b50',),

            new_root)

        self.assertHasEmptyMap(chk_bytes)

        # The update should have left us with an in memory root node, with an

        # updated key.

        self.assertEqual(new_root, chkmap._root_node._key)

    def test_iteritems_empty(self):

        chk_bytes = self.get_chk_bytes()

        root_key = CHKMap.from_dict(chk_bytes, {})

        chkmap = CHKMap(chk_bytes, root_key)

        self.assertEqual([], list(chkmap.iteritems()))

    def test_iteritems_two_items(self):

        chk_bytes = self.get_chk_bytes()

        root_key = CHKMap.from_dict(chk_bytes,

            {"a":"content here", "b":"more content"})

        chkmap = CHKMap(chk_bytes, root_key)

        self.assertEqual([("a", "content here"), ("b", "more content")],

            sorted(list(chkmap.iteritems())))

    def test_iteritems_selected_one_of_two_items(self):

        chkmap = self._get_map( {"a":"content here", "b":"more content"})

        self.assertEqual([("a", "content here")],

            sorted(list(chkmap.iteritems(["a"]))))

    def test___len__empty(self):

        chkmap = self._get_map({})

        self.assertEqual(0, len(chkmap))

    def test___len__2(self):

        chkmap = self._get_map({"foo":"bar", "gam":"quux"})

        self.assertEqual(2, len(chkmap))

    def test_max_size_100_bytes_new(self):

        # When there is a 100 byte upper node limit, a tree is formed.

        chkmap = self._get_map({("k1"*50,):"v1", ("k2"*50,):"v2"}, maximum_size=100)

        # We expect three nodes:

        # A root, with two children, and with two key prefixes - k1 to one, and

        # k2 to the other as our node splitting is only just being developed.

        # The maximum size should be embedded

        chkmap._ensure_root()

        self.assertEqual(100, chkmap._root_node.maximum_size)

        self.assertEqual(1, chkmap._root_node._key_width)

        # There should be two child nodes, and prefix of 2(bytes):

        self.assertEqual(2, len(chkmap._root_node._items))

        self.assertEqual("k", chkmap._root_node.unique_serialised_prefix())

        # The actual nodes pointed at will change as serialisers change; so

        # here we test that the key prefix is correct; then load the nodes and

        # check they have the right pointed at key; whether they have the

        # pointed at value inline or not is also unrelated to this test so we

        # don't check that in detail - rather we just check the aggregate

        # value.

        nodes = sorted(chkmap._root_node._items.items())

        ptr1 = nodes[0]

        ptr2 = nodes[1]

        self.assertEqual('k1', ptr1[0])

        self.assertEqual('k2', ptr2[0])

        node1 = _deserialise(chkmap._read_bytes(ptr1[1]), ptr1[1])

        self.assertIsInstance(node1, LeafNode)

        self.assertEqual(1, len(node1))

        self.assertEqual({('k1'*50,): 'v1'}, self.to_dict(node1, chkmap._store))

        node2 = _deserialise(chkmap._read_bytes(ptr2[1]), ptr2[1])

        self.assertIsInstance(node2, LeafNode)

        self.assertEqual(1, len(node2))

        self.assertEqual({('k2'*50,): 'v2'}, self.to_dict(node2, chkmap._store))

        # Having checked we have a good structure, check that the content is

        # still accessible.

        self.assertEqual(2, len(chkmap))

        self.assertEqual({("k1"*50,): "v1", ("k2"*50,): "v2"},

            self.to_dict(chkmap))

    def test_init_root_is_LeafNode_new(self):

        chk_bytes = self.get_chk_bytes()

        chkmap = CHKMap(chk_bytes, None)

        self.assertIsInstance(chkmap._root_node, LeafNode)

        self.assertEqual({}, self.to_dict(chkmap))

        self.assertEqual(0, len(chkmap))

    def test_init_and_save_new(self):

        chk_bytes = self.get_chk_bytes()

        chkmap = CHKMap(chk_bytes, None)

        key = chkmap._save()

        leaf_node = LeafNode()

        self.assertEqual([key], leaf_node.serialise(chk_bytes))

    def test_map_first_item_new(self):

        chk_bytes = self.get_chk_bytes()

        chkmap = CHKMap(chk_bytes, None)

        chkmap.map(("foo,",), "bar")

        self.assertEqual({('foo,',): 'bar'}, self.to_dict(chkmap))

        self.assertEqual(1, len(chkmap))

        key = chkmap._save()

        leaf_node = LeafNode()

        leaf_node.map(chk_bytes, ("foo,",), "bar")

        self.assertEqual([key], leaf_node.serialise(chk_bytes))

    def test_unmap_last_item_root_is_leaf_new(self):

        chkmap = self._get_map({("k1"*50,): "v1", ("k2"*50,): "v2"})

        chkmap.unmap(("k1"*50,))

        chkmap.unmap(("k2"*50,))

        self.assertEqual(0, len(chkmap))

        self.assertEqual({}, self.to_dict(chkmap))

        key = chkmap._save()

        leaf_node = LeafNode()

        self.assertEqual([key], leaf_node.serialise(chkmap._store))

class TestRootNode(TestCaseWithTransport):

    def test__current_size(self):

        node = RootNode()

        self.assertEqual(15, node._current_size())

        node.add_child("cd", ("sha1:12345",))

        self.assertEqual(29, node._current_size())

        self.assertEqual(29, len(node.serialise()))

        node.add_child("cd", ("sha1:123456",))

        self.assertEqual(30, node._current_size())

        self.assertEqual(30, len(node.serialise()))

        node.remove_child("cd")

        self.assertEqual(15, node._current_size())

        self.assertEqual(15, len(node.serialise()))

        node.set_maximum_size(100)

        self.assertEqual(17, node._current_size())

    def test_serialise_empty(self):

        node = RootNode()

        bytes = node.serialise()

        self.assertEqual("chkroot:\n0\n0\n0\n", bytes)

    def test_add_child_over_limit(self):

        node = RootNode()

        node.set_maximum_size(20)

        node.add_child("abcdef", ("sha1:12345",))

        size = node._current_size()

        self.assertTrue(20 < size)

        self.assertEqual(False, node.add_child("12345", ("sha1:34",)))

        # Nothing should have changed

        self.assertEqual(size, node._current_size())

        self.assertEqual(1, len(node))

    def test_add_child_resets_key(self):

        node = RootNode()

        node._key = ("something",)

        node.add_child("c", ("sha1:1234",))

        self.assertEqual(None, node._key)

    def test_add_child_returns_True(self):

        node = RootNode()

        node._key = ("something",)

        self.assertEqual(True, node.add_child("c", ("sha1:1234",)))

    def test_add_child_increases_len(self):

        node = RootNode()

        node._key = ("something",)

        node.add_child("c", ("sha1:1234",))

        self.assertEqual(1, len(node))

    def test_remove_child_decreases_len(self):

        node = RootNode()

        node.add_child("c", ("sha1:1234",))

        node._key = ("something",)

        node.remove_child("c")

        self.assertEqual(0, len(node))

    def test_remove_child_removes_child(self):

        node = RootNode()

        node.add_child("a", ("sha1:4321",))

        node.add_child("c", ("sha1:1234",))

        node._key = ("something",)

        node.remove_child("a")

        self.assertEqual({"c":("sha1:1234",)}, node._nodes)

    def test_remove_child_resets_key(self):

        node = RootNode()

        node.add_child("c", ("sha1:1234",))

        node._key = ("something",)

        node.remove_child("c")

        self.assertEqual(None, node._key)

    def test_deserialise(self):

        # deserialising from a bytestring & key sets the nodes and the known

        # key.

        node = RootNode()

        node.deserialise("chkroot:\n0\n0\n1\nc\x00sha1:1234\n", ("foo",))

        self.assertEqual({"c": ("sha1:1234",)}, node._nodes)

        self.assertEqual(("foo",), node._key)

        self.assertEqual(1, len(node))

        self.assertEqual(0, node.maximum_size)

    def test_serialise_with_child(self):

        node = RootNode()

        node.add_child("c", ("sha1:1234",))

        bytes = node.serialise()

        # type 0-max-length 1-value key\x00CHK

        self.assertEqual("chkroot:\n0\n0\n1\nc\x00sha1:1234\n", bytes)

    def test_deserialise_max_size(self):

        node = RootNode()

        node.deserialise("chkroot:\n100\n0\n1\nc\x00sha1:1234\n", ("foo",))

        self.assertEqual(100, node.maximum_size)

    def test_deserialise_key_prefix(self):

        node = RootNode()

        node.deserialise("chkroot:\n100\n10\n1\nc\x00sha1:1234\n", ("foo",))

        self.assertEqual(10, node.prefix_width)

class TestValueNode(TestCaseWithTransport):

    def test_deserialise(self):

        node = ValueNode.deserialise("chkvalue:\nfoo bar baz\n")

        self.assertEqual("foo bar baz\n", node.value)

    def test_serialise(self):

        node = ValueNode("b")

        bytes = node.serialise()

        self.assertEqual("chkvalue:\nb", bytes)

class TestLeafNode(TestCaseWithStore):

    def test_current_size_empty(self):

        node = LeafNode()

        self.assertEqual(15, node._current_size())

    def test_current_size_size_changed(self):

        node = LeafNode()

        node.set_maximum_size(10)

        self.assertEqual(16, node._current_size())

    def test_current_size_width_changed(self):

        node = LeafNode()

        node._key_width = 10

        self.assertEqual(16, node._current_size())

    def test_current_size_items(self):

        node = LeafNode()

        base_size = node._current_size()

        node = node.map(("foo bar",), "baz")

        self.assertEqual(base_size + 12, node._current_size())

    def test_deserialise_empty(self):

        node = LeafNode.deserialise("chkleaf:\n10\n1\n0\n", ("sha1:1234",))

        self.assertEqual(0, len(node))

        self.assertEqual(10, node.maximum_size)

        self.assertEqual(("sha1:1234",), node.key())

    def test_deserialise_items(self):

        node = LeafNode.deserialise(

            "chkleaf:\n0\n1\n2\nfoo bar\x00baz\nquux\x00blarh\n", ("sha1:1234",))

        self.assertEqual(2, len(node))

        self.assertEqual([(("foo bar",), "baz"), (("quux",), "blarh")],

            sorted(node.iteritems()))

    def test_iteritems_selected_one_of_two_items(self):

        node = LeafNode.deserialise(

            "chkleaf:\n0\n1\n2\nfoo bar\x00baz\nquux\x00blarh\n", ("sha1:1234",))

        self.assertEqual(2, len(node))

        self.assertEqual([(("quux",), "blarh")],

            sorted(node.iteritems([("quux",), ("qaz",)])))

    def test_key_new(self):

        node = LeafNode()

        self.assertEqual(None, node.key())

    def test_key_after_map(self):

        node = LeafNode.deserialise("chkleaf:\n10\n1\n0\n", ("sha1:1234",))

        node = node.map(("foo bar",), "baz quux")

        self.assertEqual(None, node.key())

    def test_key_after_unmap(self):

        node = LeafNode.deserialise(

            "chkleaf:\n0\n1\n2\nfoo bar\x00baz\nquux\x00blarh\n", ("sha1:1234",))

        node = node.unmap(("foo bar",))

        self.assertEqual(None, node.key())

    def test_map_exceeding_max_size_only_entry_new(self):

        node = LeafNode()

        node.set_maximum_size(10)

        result = node.map(None, ("foo bar",), "baz quux")

        self.assertEqual(("foo bar", [("", node)]), result)

        self.assertTrue(10 < node._current_size())

    def test_map_exceeding_max_size_second_entry_early_difference_new(self):

        node = LeafNode()

        node.set_maximum_size(10)

        node.map(None, ("foo bar",), "baz quux")

        prefix, result = list(node.map(None, ("blue",), "red"))

        self.assertEqual("", prefix)

        self.assertEqual(2, len(result))

        split_chars = set([result[0][0], result[1][0]])

        self.assertEqual(set(["f", "b"]), split_chars)

        nodes = dict(result)

        node = nodes["f"]

        self.assertEqual({("foo bar",): "baz quux"}, self.to_dict(node, None))

        self.assertEqual(10, node.maximum_size)

        self.assertEqual(1, node._key_width)

        node = nodes["b"]

        self.assertEqual({("blue",): "red"}, self.to_dict(node, None))

        self.assertEqual(10, node.maximum_size)

        self.assertEqual(1, node._key_width)

    def test_map_exceeding_max_size_second_entry_last_octect_changed(self):

        node = LeafNode()

        node.set_maximum_size(10)

        node = node.map(None, ("foo bar",), "baz quux")

        result = node.map(None, ("foo baz",), "red")

        self.assertIsInstance(result, InternalNode)

        # should have copied the data in:

        self.assertEqual(2, len(result))

        self.assertEqual({('foo baz',): 'red', ('foo bar',): 'baz quux'},

            self.to_dict(result))

        self.assertEqual(10, result.maximum_size)

        self.assertEqual(1, result._key_width)

    def test_map_first(self):

        node = LeafNode()

        result = node.map(("foo bar",), "baz quux")

        self.assertEqual(result, node)

        self.assertEqual({("foo bar",):"baz quux"}, self.to_dict(node))

        self.assertEqual(1, len(node))

    def test_map_second(self):

        node = LeafNode()

        node = node.map(("foo bar",), "baz quux")

        result = node.map(("bingo",), "bango")

        self.assertEqual(result, node)

        self.assertEqual({("foo bar",):"baz quux", ("bingo",):"bango"},

            self.to_dict(node))

        self.assertEqual(2, len(node))

    def test_map_replacement(self):

        node = LeafNode()

        node = node.map(("foo bar",), "baz quux")

        result = node.map(("foo bar",), "bango")

        self.assertEqual(result, node)

        self.assertEqual({("foo bar",): "bango"},

            self.to_dict(node))

        self.assertEqual(1, len(node))

    def test_serialise_empty(self):

        store = self.get_chk_bytes()

        node = LeafNode()

        node.set_maximum_size(10)

        expected_key = ("sha1:62cc3565b48b0e830216e652cf99c6bd6b05b4b9",)

        self.assertEqual([expected_key],

            list(node.serialise(store)))

        self.assertEqual("chkleaf:\n10\n1\n0\n", self.read_bytes(store, expected_key))

        self.assertEqual(expected_key, node.key())

    def test_serialise_items(self):

        store = self.get_chk_bytes()

        node = LeafNode()

        node.set_maximum_size(10)

        node = node.map(("foo bar",), "baz quux")

        expected_key = ("sha1:d44cb6f0299b7e047da7f9e98f810e98f1dce1a7",)

        self.assertEqual([expected_key],

            list(node.serialise(store)))

        self.assertEqual("chkleaf:\n10\n1\n1\nfoo bar\x00baz quux\n",

            self.read_bytes(store, expected_key))

        self.assertEqual(expected_key, node.key())

    def test_unique_serialised_prefix_empty_new(self):

        node = LeafNode()

        self.assertEqual("", node.unique_serialised_prefix())

        return

    def test_unique_serialised_prefix_one_item_new(self):

        node = LeafNode()

        result = node.map(None, ("foo bar", "baz"), "baz quux")

        self.assertEqual("foo bar\x00baz", node.unique_serialised_prefix())

    def test_unmap_missing(self):

        node = LeafNode()

        self.assertRaises(KeyError, node.unmap, ("foo bar",))

    def test_unmap_present(self):

        node = LeafNode()

        node = node.map(None, ("foo bar",), "baz quux")

        result = node.unmap(("foo bar",))

        self.assertEqual(result, node)

        self.assertEqual({}, self.to_dict(node))

        self.assertEqual(0, len(node))

class TestInternalNode(TestCaseWithStore):

    def test_add_node_empty_new(self):

        node = InternalNode()

        child = LeafNode()

        child.set_maximum_size(100)

        child.map(None, ("foo",), "bar")

        node.add_node("foo", child)

        # Note that node isn't strictly valid now as a tree (only one child),

        # but thats ok for this test.

        # The first child defines the node's width:

        self.assertEqual(3, node._node_width)

        # We should be able to iterate over the contents without doing IO.

        self.assertEqual({('foo',): 'bar'}, self.to_dict(node, None))

        # The length should be known:

        self.assertEqual(1, len(node))

        # serialising the node should serialise the child and the node.

        chk_bytes = self.get_chk_bytes()

        keys = list(node.serialise(chk_bytes))

        child_key = child.serialise(chk_bytes)[0]

        self.assertEqual(

            [child_key, ('sha1:db23b260c2bf46bf7446c39f91668900a2491610',)],

            keys)

        # We should be able to access deserialised content.

        bytes = self.read_bytes(chk_bytes, keys[1])

        node = _deserialise(bytes, keys[1])

        self.assertEqual(1, len(node))

        self.assertEqual({('foo',): 'bar'}, self.to_dict(node, chk_bytes))

        self.assertEqual(3, node._node_width)

    def test_add_node_resets_key_new(self):

        node = InternalNode()

        child = LeafNode()

        child.set_maximum_size(100)

        child.map(None, ("foo",), "bar")

        node.add_node("foo", child)

        chk_bytes = self.get_chk_bytes()

        keys = list(node.serialise(chk_bytes))

        self.assertEqual(keys[1], node._key)

        node.add_node("fos", child)

        self.assertEqual(None, node._key)

#    def test_add_node_empty_oversized_one_ok_new(self):

#    def test_add_node_one_oversized_second_kept_minimum_fan(self):

#    def test_add_node_two_oversized_third_kept_minimum_fan(self):

#    def test_add_node_one_oversized_second_splits_errors(self):

    def test_add_node_empty_oversized_no_common_sets_prefix(self):

        # adding a node with two children that is oversized will generate two

        # new leaf nodes, and a prefix width that cuts one byte off the longest

        # key (because that is sufficient to guarantee a split

        overpacked = LeafNode()

        overpacked.set_maximum_size(10)

        overpacked.map(None, ("foo bar",), "baz")

        overpacked.map(None, ("strange thing",), "it is")

        # at this point, map returned a new internal node that is already

        # packed, but that should have preserved the old node due to the 

        # functional idioms.. check to be sure:

        self.assertTrue(overpacked.maximum_size < overpacked._current_size())

        node = InternalNode()

        # We're not testing that the internal node rebalances yet

        node.set_maximum_size(0)

        node._add_node(overpacked)

        # 13 is the length of strange_thing serialised; as there is no node size

        # set, we pack the internal node as densely as possible.

        self.assertEqual(13, node._node_width)

        self.assertEqual(set(["strange thing", "foo bar\x00\x00\x00\x00\x00\x00"]),

            set(node._items.keys()))

        self.assertEqual(2, len(node))

        self.assertEqual({('strange thing',): 'it is'},

            self.to_dict(node._items["strange thing"]))

        self.assertEqual({('foo bar',): 'baz'},

            self.to_dict(node._items["foo bar\x00\x00\x00\x00\x00\x00"]))

    def test_iteritems_empty_new(self):

        node = InternalNode()

        self.assertEqual([], sorted(node.iteritems(None)))

    def test_iteritems_two_children(self):

        node = InternalNode()

        leaf1 = LeafNode()

        leaf1.map(None, ('foo bar',), 'quux')

        leaf2 = LeafNode()

        leaf2 = LeafNode()

        leaf2.map(None, ('strange',), 'beast')

        node._items['foo ba'] = leaf1

        node._items['strang'] = leaf2

        self.assertEqual([(('foo bar',), 'quux'), (('strange',), 'beast')],

            sorted(node.iteritems()))

    def test_iteritems_two_children_partial(self):

        node = InternalNode()

        leaf2 = LeafNode()

        leaf2 = LeafNode()

        leaf2.map(None, ('strange',), 'beast')

        # This sets up a path that should not be followed - it will error if

        # the code tries to.

        node._items['foo ba'] = None

        node._items['strang'] = leaf2

        node._node_width = 6

        self.assertEqual([(('strange',), 'beast')],

            sorted(node.iteritems([('strange',), ('weird',)])))

    def test_iteritems_partial_empty(self):

        node = InternalNode()

        self.assertEqual([], sorted(node.iteritems([('missing',)])))

    def test_map_to_existing_child(self):

        # mapping a new key which is in a child of an internal node maps

        # recursively.

        overpacked = LeafNode()

        overpacked.set_maximum_size(10)

        overpacked.map(None, ("foo bar",), "baz")

        node = overpacked.map(None, ("foo baz",), "it is")

        self.assertIsInstance(node, InternalNode)

        # Now, increase the maximum size limit on the subnode for foo bar

        child = node._items[node._serialised_key(("foo bar",))]

        child.set_maximum_size(200)

        # And map a new key into node, which will land in the same child node

        result = node.map(None, ("foo bar baz",), "new value")