diff --git a/osc_placement/tests/functional/base.py b/osc_placement/tests/functional/base.py
index 49ebc4d..a40c291 100644
--- a/osc_placement/tests/functional/base.py
+++ b/osc_placement/tests/functional/base.py
@@ -80,7 +80,8 @@ class BaseTestCase(base.BaseTestCase):
         for name in RESET_LOGGING:
             logging.getLogger(name).setLevel(logging.WARNING)
 
-    def openstack(self, cmd, may_fail=False, use_json=False):
+    def openstack(self, cmd, may_fail=False, use_json=False,
+                  may_print_to_stderr=False):
         to_exec = []
         # Make all requests as a noauth admin user.
         to_exec += [
@@ -110,17 +111,30 @@ class BaseTestCase(base.BaseTestCase):
             except SystemExit as exc:
                 return_code = exc.code
 
+        # We may have error/warning messages in stderr, so treat it
+        # separately from the stdout.
+        output = self.output.getvalue()
+        error = self.error.getvalue()
+
         if return_code:
-            msg = 'Command: "%s"\noutput: %s' % (' '.join(to_exec),
-                                                 self.error.getvalue())
+            msg = 'Command: "%s"\noutput: %s' % (' '.join(to_exec), error)
             if not may_fail:
                 raise CommandException(msg, cmd=' '.join(to_exec))
 
-        output = self.output.getvalue() + self.error.getvalue()
         if use_json and output:
-            return json.loads(output)
-        else:
-            return output
+            output = json.loads(output)
+
+        if may_print_to_stderr:
+            return output, error
+
+        if error:
+            msg = ('Test code error - The command did not fail but it '
+                   'has a warning message. Set the "may_print_to_stderr" '
+                   'argument to true to get and validate the message:\n'
+                   'Command: "%s"\nstderr: %s') % (
+                ' '.join(to_exec), error)
+            raise CommandException(msg, cmd=' '.join(to_exec))
+        return output
 
     def rand_name(self, name='', prefix=None):
         """Generate a random name that includes a random number
@@ -221,7 +235,7 @@ class BaseTestCase(base.BaseTestCase):
 
     def resource_allocation_set(self, consumer_uuid, allocations,
                                 project_id=None, user_id=None,
-                                use_json=True):
+                                use_json=True, may_print_to_stderr=False):
         cmd = 'resource provider allocation set {allocs} {uuid}'.format(
             uuid=consumer_uuid,
             allocs=' '.join('--allocation {}'.format(a) for a in allocations)
@@ -230,7 +244,8 @@ class BaseTestCase(base.BaseTestCase):
             cmd += ' --project-id %s' % project_id
         if user_id:
             cmd += ' --user-id %s' % user_id
-        result = self.openstack(cmd, use_json=use_json)
+        result = self.openstack(cmd, use_json=use_json,
+                                may_print_to_stderr=may_print_to_stderr)
 
         def cleanup(uuid):
             try:
diff --git a/osc_placement/tests/functional/test_allocation.py b/osc_placement/tests/functional/test_allocation.py
index bd2b5bd..68d06d5 100644
--- a/osc_placement/tests/functional/test_allocation.py
+++ b/osc_placement/tests/functional/test_allocation.py
@@ -54,17 +54,22 @@ class TestAllocation(base.BaseTestCase):
         self.assertEqual(expected, retrieved_alloc)
 
         # Test that specifying --project-id and --user-id before microversion
-        # 1.8 does not result in an error (they will be ignored). We have
-        # to specify use_json=False because there will be a warning in the
-        # output which can't be json-decoded.
-        output = self.resource_allocation_set(
+        # 1.8 does not result in an error but display a warning.
+        output, warning = self.resource_allocation_set(
             consumer_uuid,
             ['rp={},VCPU=2'.format(self.rp1['uuid']),
              'rp={},MEMORY_MB=512'.format(self.rp1['uuid'])],
-            project_id='fake-project', user_id='fake-user', use_json=False)
+            project_id='fake-project', user_id='fake-user',
+            may_print_to_stderr=True)
+        expected = [
+            {'resource_provider': self.rp1['uuid'],
+             'generation': 3,
+             'resources': {'VCPU': 2, 'MEMORY_MB': 512}}
+        ]
+        self.assertEqual(expected, output)
         self.assertIn(
             '--project-id and --user-id options do not affect allocation for '
-            '--os-placement-api-version less than 1.8', output)
+            '--os-placement-api-version less than 1.8', warning)
 
     def test_allocation_create_empty(self):
         consumer_uuid = str(uuid.uuid4())