diff --git a/functional/test_instance_group.py b/functional/test_instance_group.py
index 02a2858..e8f0309 100644
--- a/functional/test_instance_group.py
+++ b/functional/test_instance_group.py
@@ -27,7 +27,8 @@
   "Parameters" : {"size": {"Type": "String", "Default": "1"},
                   "AZ": {"Type": "String", "Default": "nova"},
                   "image": {"Type": "String"},
-                  "flavor": {"Type": "String"}},
+                  "flavor": {"Type": "String"},
+                  "user_data": {"Type": "String", "Default": "jsconfig data"}},
   "Resources": {
     "JobServerGroup": {
       "Type": "OS::Heat::InstanceGroup",
@@ -45,7 +46,7 @@
         "ImageId"           : {"Ref": "image"},
         "InstanceType"      : {"Ref": "flavor"},
         "SecurityGroups"    : [ "sg-1" ],
-        "UserData"          : "jsconfig data"
+        "UserData"          : {"Ref": "user_data"}
       }
     }
   },
@@ -71,7 +72,7 @@
   random1:
     type: OS::Heat::RandomString
     properties:
-      salt: {get_param: ImageId}
+      salt: {get_param: UserData}
 outputs:
   PublicIp:
     value: {get_attr: [random1, value]}
@@ -105,8 +106,6 @@
 
     def setUp(self):
         super(InstanceGroupTest, self).setUp()
-        if not self.conf.image_ref:
-            raise self.skipException("No image configured to test")
         if not self.conf.minimal_image_ref:
             raise self.skipException("No minimal image configured to test")
         if not self.conf.instance_type:
@@ -141,7 +140,7 @@
         files = {'provider.yaml': self.instance_template}
         env = {'resource_registry': {'AWS::EC2::Instance': 'provider.yaml'},
                'parameters': {'size': 4,
-                              'image': self.conf.image_ref,
+                              'image': self.conf.minimal_image_ref,
                               'flavor': self.conf.instance_type}}
         stack_identifier = self.stack_create(template=self.template,
                                              files=files, environment=env)
@@ -158,7 +157,7 @@
         files = {'provider.yaml': self.instance_template}
         env = {'resource_registry': {'AWS::EC2::Instance': 'provider.yaml'},
                'parameters': {'size': 2,
-                              'image': self.conf.image_ref,
+                              'image': self.conf.minimal_image_ref,
                               'flavor': self.conf.instance_type}}
 
         stack_identifier = self.stack_create(template=self.template,
@@ -170,7 +169,7 @@
         # Increase min size to 5
         env2 = {'resource_registry': {'AWS::EC2::Instance': 'provider.yaml'},
                 'parameters': {'size': 5,
-                               'image': self.conf.image_ref,
+                               'image': self.conf.minimal_image_ref,
                                'flavor': self.conf.instance_type}}
         self.update_stack(stack_identifier, self.template,
                           environment=env2, files=files)
@@ -187,7 +186,7 @@
         env = {'resource_registry':
                {'AWS::EC2::Instance': 'provider.yaml'},
                'parameters': {'size': 1,
-                              'image': self.conf.image_ref,
+                              'image': self.conf.minimal_image_ref,
                               'flavor': self.conf.instance_type}}
 
         stack_identifier = self.stack_create(template=self.template,
@@ -200,8 +199,9 @@
                 {'AWS::EC2::Instance': 'provider.yaml'},
                 'parameters': {'size': '2',
                                'AZ': 'wibble',
-                               'image': self.conf.image_ref,
-                               'flavor': self.conf.instance_type}}
+                               'image': self.conf.minimal_image_ref,
+                               'flavor': self.conf.instance_type,
+                               'user_data': 'new data'}}
         self.update_stack(stack_identifier, self.template,
                           environment=env2, files=files)
 
@@ -219,7 +219,7 @@
         files = {'provider.yaml': self.bad_instance_template}
         env = {'resource_registry': {'AWS::EC2::Instance': 'provider.yaml'},
                'parameters': {'size': 2,
-                              'image': self.conf.image_ref,
+                              'image': self.conf.minimal_image_ref,
                               'flavor': self.conf.instance_type}}
 
         self.client.stacks.create(
@@ -254,7 +254,7 @@
         files = {'provider.yaml': self.instance_template}
         env = {'resource_registry': {'AWS::EC2::Instance': 'provider.yaml'},
                'parameters': {'size': 2,
-                              'image': self.conf.image_ref,
+                              'image': self.conf.minimal_image_ref,
                               'flavor': self.conf.instance_type}}
 
         stack_identifier = self.stack_create(template=self.template,
@@ -323,8 +323,8 @@
         size = 5
         env = {'resource_registry': {'AWS::EC2::Instance': 'provider.yaml'},
                'parameters': {'size': size,
-                              'image': self.conf.image_ref,
-                              'flavor': self.conf.instance_type}}
+                              'image': self.conf.minimal_image_ref,
+                              'flavor': self.conf.minimal_instance_type}}
         stack_name = self._stack_rand_name()
         stack_identifier = self.stack_create(
             stack_name=stack_name,
@@ -394,7 +394,7 @@
         policy['MinInstancesInService'] = '1'
         policy['MaxBatchSize'] = '3'
         config = updt_template['Resources']['JobServerConfig']
-        config['Properties']['ImageId'] = self.conf.minimal_image_ref
+        config['Properties']['UserData'] = 'new data'
 
         self.update_instance_group(updt_template,
                                    num_updates_expected_on_updt=5,
@@ -414,7 +414,7 @@
         policy['MinInstancesInService'] = '4'
         policy['MaxBatchSize'] = '4'
         config = updt_template['Resources']['JobServerConfig']
-        config['Properties']['ImageId'] = self.conf.minimal_image_ref
+        config['Properties']['UserData'] = 'new data'
 
         self.update_instance_group(updt_template,
                                    num_updates_expected_on_updt=2,
@@ -430,7 +430,7 @@
         policy['MinInstancesInService'] = '0'
         policy['MaxBatchSize'] = '20'
         config = updt_template['Resources']['JobServerConfig']
-        config['Properties']['ImageId'] = self.conf.minimal_image_ref
+        config['Properties']['UserData'] = 'new data'
 
         self.update_instance_group(updt_template,
                                    num_updates_expected_on_updt=5,
@@ -447,7 +447,7 @@
         policy['MaxBatchSize'] = '2'
         policy['PauseTime'] = 'PT0S'
         config = updt_template['Resources']['JobServerConfig']
-        config['Properties']['ImageId'] = self.conf.minimal_image_ref
+        config['Properties']['UserData'] = 'new data'
 
         self.update_instance_group(updt_template,
                                    num_updates_expected_on_updt=3,