new file mode 100644
--- /dev/null
+++ b/tests/test_revmap_migrate.py
@@ -0,0 +1,68 @@
+import test_util
+
+from mercurial import util as hgutil
+from hgsubversion import svnmeta, maps
+from mercurial.node import hex
+
+class TestRevMapMigrate(test_util.TestBase):
+
+    def _test_revmap_migrate(self, fromclass, toclass):
+        # revmap interfaces to test
+        getters = [
+            lambda x: x.branchedits('the_branch', 3),
+            lambda x: x.branchedits('the_branch', 4),
+            lambda x: x.branchedits('the_branch', 5),
+            lambda x: x.branchedits('the_branch', 6),
+            lambda x: x.branchedits(None, 5),
+            lambda x: x.branchedits('non_existed', 10),
+            lambda x: x.branchmaxrevnum('the_branch', 3),
+            lambda x: x.branchmaxrevnum('the_branch', 4),
+            lambda x: x.branchmaxrevnum('the_branch', 5),
+            lambda x: x.branchmaxrevnum('the_branch', 6),
+            lambda x: x.branchmaxrevnum(None, 5),
+            lambda x: x.branchmaxrevnum('non_existed', 10),
+            lambda x: list(x.revhashes(3)),
+            lambda x: list(x.revhashes(4)),
+            lambda x: list(x.revhashes(42)),
+            lambda x: list(x.revhashes(105)),
+            lambda x: x.firstpulled,
+            lambda x: x.lastpulled,
+            lambda x: x.lasthash,
+        ]
+
+        svnmeta.SVNMeta._defaultrevmapclass = fromclass
+        repo = self._load_fixture_and_fetch('two_heads.svndump')
+        meta = svnmeta.SVNMeta(repo)
+        self.assertEqual(meta.revmap.__class__, fromclass)
+        origrevmap = meta.revmap
+
+        # insert fake special (duplicated, with '\0') data
+        origrevmap[103, None] = b'\0' * 20
+        origrevmap[104, None] = b'\0' * 18 + b'cd'
+        origrevmap[105, None] = b'ab\0cdefghijklmnopqrs'
+        origrevmap[104, None] = b'\0' * 18 + b'\xff\0'
+        origrevmap[105, 'ab'] = origrevmap[105, None]
+
+        origvalues = [f(meta.revmap) for f in getters]
+
+        # migrate to another format (transparently)
+        svnmeta.SVNMeta._defaultrevmapclass = toclass
+        meta = svnmeta.SVNMeta(repo)
+        self.assertEqual(meta.revmap.__class__, toclass)
+
+        # enable iteration otherwise we cannot use iteritems
+        origrevmap._allowiter = True
+        for k, v in origrevmap.iteritems():
+            newv = meta.revmap[k]
+            self.assertEqual(newv, v)
+            self.assertEqual(len(newv), 20)
+            self.assertEqual(meta.revmap[meta.revmap.hashes()[v]], v)
+
+        newvalues = [f(meta.revmap) for f in getters]
+        self.assertEqual(origvalues, newvalues)
+
+    def test_revmap_migrate_up(self):
+        self._test_revmap_migrate(maps.RevMap, maps.SqliteRevMap)
+
+    def test_revmap_migrate_down(self):
+        self._test_revmap_migrate(maps.SqliteRevMap, maps.RevMap)