Add functional test for chained substitution

This adds a functional test for chained substitution.

For this test to pass a subtle bug had to be fixed in
the code in DocumentDict wrapper. It was possible for
instances of this class to return a NEW object when
`self.data` was invoked causing
`substitution_src.data.update(data)` to fail when
attempting to update a substitution source with updated
layered data because -- if data={} at that moment in time --
the code in DocumentDict would return a NEW object {}.

This was because `self.get('data') or {}` would return {}
on the RHS instead of self['data'] because self['data']
itself would be {} which would evaluate to false in terms
of truthiness resulting in the wrong object ref being returned...
essentially causing the update to fail. This has been
fixed.

Change-Id: I23ad0010e1d7df73e8e1a1456ba21b3e611bb0dd

deckhand/control/revision_documents.py

@@ -113,7 +113,8 @@ class RenderedDocumentsResource(api_base.BaseResource):
             # been pre-validated during ingestion. Documents are post-validated
             # below, regardless.
             document_layering = layering.DocumentLayering(
-                documents, substitution_sources, validate=False)
+                documents, substitution_sources=substitution_sources,
+                validate=False)
             rendered_documents = document_layering.render()
         except (errors.InvalidDocumentLayer,
                 errors.InvalidDocumentParent,

deckhand/engine/document_wrapper.py

@@ -39,15 +39,18 @@ class DocumentDict(dict):
 
     @property
     def schema(self):
-        return self.get('schema') or ''
+        schema = self.get('schema')
+        return schema if schema is not None else ''
 
     @property
     def metadata(self):
-        return self.get('metadata') or {}
+        metadata = self.get('metadata')
+        return metadata if metadata is not None else {}
 
     @property
     def data(self):
-        return self.get('data') or {}
+        data = self.get('data')
+        return data if data is not None else {}
 
     @data.setter
     def data(self, value):

deckhand/tests/functional/gabbits/chained-substitution.yaml

@@ -0,0 +1,51 @@
+# Tests to verify "chained" substitution from document A -> B -> C
+#
+# 1. Purges existing data to ensure test isolation
+# 2. Creates a new revision with documents in it.
+# 3. Verifies first substitution (A -> B)
+# 4. Verifies second substitution (B -> C)
+
+defaults:
+  request_headers:
+    content-type: application/x-yaml
+  response_headers:
+    content-type: application/x-yaml
+
+tests:
+  - name: purge
+    desc: Begin testing from known state.
+    DELETE: /api/v1.0/revisions
+    status: 204
+    response_headers: null
+
+  - name: create
+    desc: Create documents.
+    PUT: /api/v1.0/buckets/mop/documents
+    status: 200
+    data: <@resources/chained-substitution.yaml
+
+  - name: verify_intermediate_substitution
+    desc: Check for chained substitution
+    GET: /api/v1.0/revisions/$RESPONSE['$.[0].status.revision']/rendered-documents
+    query_parameters:
+      sort: schema
+    status: 200
+    query_parameters:
+      schema: example/Middle/v1
+    response_multidoc_jsonpaths:
+      $.`len`: 1
+      $.[0].data:
+        mid_key: original-data
+
+  - name: verify_final_substitution
+    desc: Check for chained substitution
+    GET: /api/v1.0/revisions/$RESPONSE['$.[0].status.revision']/rendered-documents
+    query_parameters:
+      sort: schema
+    status: 200
+    query_parameters:
+      schema: example/Dest/v1
+    response_multidoc_jsonpaths:
+      $.`len`: 1
+      $.[0].data:
+        dest_key: original-data

deckhand/tests/functional/gabbits/resources/chained-substitution.yaml

@@ -0,0 +1,50 @@
+---
+schema: deckhand/LayeringPolicy/v1
+metadata:
+  schema: metadata/Control/v1
+  name: layering-policy
+data:
+  layerOrder:
+    - one
+---
+schema: example/Source/v1
+metadata:
+  schema: metadata/Document/v1
+  name: source
+  layeringDefinition:
+    abstract: false
+    layer: one
+data: original-data
+---
+schema: example/Middle/v1
+metadata:
+  schema: metadata/Document/v1
+  name: middle
+  layeringDefinition:
+    abstract: false
+    layer: one
+  substitutions:
+    - src:
+        schema: example/Source/v1
+        name: source
+        path: .
+      dest:
+        path: .mid_key
+data: {}
+---
+schema: example/Dest/v1
+metadata:
+  schema: metadata/Document/v1
+  name: dest
+  layeringDefinition:
+    abstract: false
+    layer: one
+  substitutions:
+    - src:
+        schema: example/Middle/v1
+        name: middle
+        path: .mid_key
+      dest:
+        path: .dest_key
+data: {}
+...