Add PATCH support for stack-update --dry-run

Previously we just passed the "existing" kwarg directly to the PUT,
which was then ignored by the API, so PATCH update preview commands
wouldn't work.  Now heat supports PATCH preview_update_stack, we
can revise this to use the PATCH method when appropriate.

Requires this heat patch for --existing --dry-run to work when used
together: https://review.openstack.org/#/c/230054

Change-Id: Ib07c0a83edfbef7a08b4af344850d0a791b7704d
Closes-Bug: #1501207

heatclient/tests/unit/test_shell.py

@@ -2315,7 +2315,7 @@ class ShellTestUserPass(ShellBase):
         for r in required:
             self.assertRegexpMatches(update_text, r)
 
-    def test_stack_update_dry_run(self):
+    def _setup_stubs_update_dry_run(self, template_file, existing=False):
         self.register_keystone_auth_fixture()
 
         resp_dict = {"stack": {
@@ -2336,7 +2336,6 @@ class ShellTestUserPass(ShellBase):
             self.client.json_request(
                 'GET', '/stacks/teststack2/2').AndReturn((resp, resp_dict))
 
-        template_file = os.path.join(TEST_VAR_DIR, 'minimal.template')
         template_data = open(template_file).read()
 
         replaced_res = {"resource_name": "my_res",
@@ -2375,22 +2374,50 @@ class ShellTestUserPass(ShellBase):
             'environment': {},
             'template': jsonutils.loads(template_data),
             'parameters': {'"KeyPairName': 'updated_key"'},
-            'disable_rollback': False,
-            'existing': True}
+            'disable_rollback': False}
+
+        if existing is True:
+            method = 'PATCH'
+        else:
+            method = 'PUT'
 
         if self.client == http.SessionClient:
             self.client.request(
-                '/stacks/teststack2/2/preview', 'PUT',
+                '/stacks/teststack2/2/preview', method,
                 data=expected_data, headers={}).AndReturn(resp)
         else:
             http.HTTPClient.json_request(
-                'PUT', '/stacks/teststack2/2/preview',
+                method, '/stacks/teststack2/2/preview',
                 data=expected_data,
                 headers={'X-Auth-Key': 'password', 'X-Auth-User': 'username'}
             ).AndReturn((resp, None))
 
         self.m.ReplayAll()
 
+    def test_stack_update_dry_run(self):
+        template_file = os.path.join(TEST_VAR_DIR, 'minimal.template')
+        self._setup_stubs_update_dry_run(template_file)
+        update_preview_text = self.shell(
+            'stack-update teststack2/2 '
+            '--template-file=%s '
+            '--enable-rollback '
+            '--parameters="KeyPairName=updated_key" '
+            '--dry-run ' % template_file)
+
+        required = [
+            'stack_name',
+            'id',
+            'teststack2',
+            '2',
+            'state',
+            'replaced'
+        ]
+        for r in required:
+            self.assertRegexpMatches(update_preview_text, r)
+
+    def test_stack_update_dry_run_patch(self):
+        template_file = os.path.join(TEST_VAR_DIR, 'minimal.template')
+        self._setup_stubs_update_dry_run(template_file, existing=True)
         update_preview_text = self.shell(
             'stack-update teststack2/2 '
             '--template-file=%s '

heatclient/v1/stacks.py

@@ -151,9 +151,14 @@ class StackManager(base.BaseManager):
         """Preview a stack update."""
         s = self.get(stack_id)
         headers = self.client.credentials_headers()
-        resp = self.client.put('/stacks/%s/%s/preview' %
-                               (s.stack_name, s.id),
-                               data=kwargs, headers=headers)
+        if kwargs.pop('existing', None):
+            resp = self.client.patch('/stacks/%s/%s/preview' %
+                                     (s.stack_name, s.id),
+                                     data=kwargs, headers=headers)
+        else:
+            resp = self.client.put('/stacks/%s/%s/preview' %
+                                   (s.stack_name, s.id),
+                                   data=kwargs, headers=headers)
         body = utils.get_response_body(resp)
         return body