Add a test for graph_rql_expr() that cannot find a path

This can occur in real cases when etype is related to his parent by multiple
optional relations where only one could be filled. We could generate 'OR'
expressions but for now this is not handled.

test/data/schema.py

@@ -47,6 +47,17 @@
     inlined = True
 
 
+class BiographyComment(EntityType):
+    pass
+
+
+class commented_by(RelationDefinition):
+    subject = 'Biography'
+    object = 'BiographyComment'
+    cardinality = '*?'
+    composite = 'subject'
+
+
 class Event(EntityType):
     """Event in the life of an Agent, gathered in its Biography"""
 

test/test_compound.py

@@ -74,6 +74,9 @@
             'Biography': {
                 ('biography', 'object'): ['Agent'],
             },
+            'BiographyComment': {
+                ('commented_by', 'object'): ['Biography'],
+            },
             'Event': {
                 ('event', 'object'): ['Biography'],
                 ('relates', 'object'): ['Anecdote'],

test/test_utils.py

@@ -35,8 +35,9 @@
             ('account', 'object'),
             ('narrated_by', 'subject'),
             ('comments', 'subject'),
+            ('commented_by', 'object'),
         ])
         self.assertEqual(structurals, expected)
         expected = set([
             ('narrated_by', 'subject'),
             ('relates', 'object'),
@@ -38,8 +39,9 @@
         ])
         self.assertEqual(structurals, expected)
         expected = set([
             ('narrated_by', 'subject'),
             ('relates', 'object'),
+            ('commented_by', 'object'),
         ])
         self.assertEqual(optionals, expected)
         mandatories = [(str(rdef), role) for rdef, role in mandatories]
@@ -57,6 +59,7 @@
         optional = utils.optional_relations(self.schema, structure)
         expected = {
             'Anecdote': set([('narrated_by', 'subject')]),
+            'BiographyComment': set([('commented_by', 'object')]),
             'Event': set([('relates', 'object')]),
         }
         self.assertEqual(optional, expected)
@@ -95,6 +98,10 @@
         ):
             self.assertEqual(utils.graph_rql_expr(self.schema, graph, etype, 'Agent'),
                              expected)
+            with self.assertRaisesRegexp(
+                ValueError, '^could not find a RQL path from BiographyComment to Agent$',
+            ):
+                utils.graph_rql_expr(self.schema, graph, 'BiographyComment', 'Agent')
 
 
 if __name__ == '__main__':