On Python 3 in testMigrationTool only test upgrade from Plone 5.2.

You cannot upgrade a Plone 4.0 or 5.1 site to 5.2 or higher when you are on Python 3.
You must first migrate to 5.2 with Python 2.7.
Also, this avoids a test failure on 6.0 because the 5.0alpha upgrade calls qi.isProductInstalled, which has been removed.

Products/CMFPlone/tests/testMigrationTool.py

@@ -3,6 +3,18 @@
 from Products.CMFPlone.factory import _DEFAULT_PROFILE
 from Products.CMFCore.utils import getToolByName
 
+import sys
+
+
+if sys.version_info.major == 2:
+    # Start a test upgrade at version 2.5.
+    # The first existing upgrade step will immediately put it at 4001.
+    START_PROFILE = '2.5'
+else:
+    # Python 3 is only supported on 5.2+.
+    # This means you can not upgrade from 5.1 or earlier.
+    START_PROFILE = '5200'
+
 
 class TestMigrationTool(PloneTestCase.PloneTestCase):
 
@@ -39,8 +51,7 @@ def testListOwnUpgradeSteps(self):
 
     def testDoUpgrades(self):
         self.setRoles(['Manager'])
-
-        self.setup.setLastVersionForProfile(_DEFAULT_PROFILE, '2.5')
+        self.setup.setLastVersionForProfile(_DEFAULT_PROFILE, START_PROFILE)
         upgrades = self.migration.listUpgrades()
         self.assertGreater(len(upgrades), 0)
 
@@ -69,7 +80,7 @@ def testDoUpgrades(self):
 
     def testUpgrade(self):
         self.setRoles(['Manager'])
-        self.setup.setLastVersionForProfile(_DEFAULT_PROFILE, '2.5')
+        self.setup.setLastVersionForProfile(_DEFAULT_PROFILE, START_PROFILE)
         self.migration.upgrade()
 
         # And we have reached our current profile version
@@ -130,7 +141,7 @@ def testListUpgradeStepsNotTooNew(self):
 
     def testUpgrade(self):
         self.setRoles(['Manager'])
-        self.setup.setLastVersionForProfile(_DEFAULT_PROFILE, '2.5')
+        self.setup.setLastVersionForProfile(_DEFAULT_PROFILE, START_PROFILE)
         self.migration.upgrade()
 
         # And we have reached our current profile version