Rename VersionUpgrade plug-in from 40 to 35

Because the next version is going to be called 3.5, not 4.0.

plugins/VersionUpgrade/VersionUpgrade34to35/tests/TestVersionUpgrade34to35.py

@@ -0,0 +1,35 @@
+# Copyright (c) 2018 Ultimaker B.V.
+# Cura is released under the terms of the LGPLv3 or higher.
+
+import configparser #To parse the resulting config files.
+import pytest #To register tests with.
+
+import VersionUpgrade34to35 #The module we're testing.
+
+##  Creates an instance of the upgrader to test with.
+@pytest.fixture
+def upgrader():
+    return VersionUpgrade34to35.VersionUpgrade34to35()
+
+test_upgrade_version_nr_data = [
+    ("Empty config file",
+    """[general]
+    version = 5
+    [metadata]
+    setting_version = 4
+"""
+    )
+]
+
+##  Tests whether the version numbers are updated.
+@pytest.mark.parametrize("test_name, file_data", test_upgrade_version_nr_data)
+def test_upgradeVersionNr(test_name, file_data, upgrader):
+    #Perform the upgrade.
+    _, upgraded_instances = upgrader.upgradePreferences(file_data, "<string>")
+    upgraded_instance = upgraded_instances[0]
+    parser = configparser.ConfigParser(interpolation = None)
+    parser.read_string(upgraded_instance)
+
+    #Check the new version.
+    assert parser["general"]["version"] == "6"
+    assert parser["metadata"]["setting_version"] == "5"