With test cases.

tests/test_recursion.py

+import json
+from httmock import urlmatch, HTTMock, with_httmock, all_requests
+
+from ppp_datamodel import Resource
+from ppp_datamodel.communication import Request, TraceItem, Response
+from ppp_core.tests import PPPTestCase
+from ppp_core import app
+
+config = """
+{
+    "debug": true,
+    "modules": [
+        {
+            "name": "my_module",
+            "url": "http://test/my_module/",
+            "coefficient": 1
+        },
+        {
+            "name": "my_module2",
+            "url": "http://test/my_module2/",
+            "coefficient": 1
+        }
+    ]
+}"""
+
+@urlmatch(netloc='test', path='/my_module/')
+def my_module_mock(url, request):
+    r = Request.from_json(request.body)
+    if r.tree == Resource('one'):
+        c = '"measures": {"accuracy": 1, "relevance": 1}, "tree": {"type": "resource", "value": "two"}'
+        return {'status_code': 200,
+                'content': '[{"language": "en", %s, '
+                             '"trace": [{"module": "module1", %s}]}]' %
+                             (c, c)}
+    else:
+        return {'status_code': 200,
+                'content': '[]'}
+
+@urlmatch(netloc='test', path='/my_module2/')
+def my_module2_mock(url, request):
+    r = Request.from_json(request.body)
+    if r.tree == Resource('two'):
+        c = '"measures": {"accuracy": 1, "relevance": 2}, "tree": {"type": "resource", "value": "three"}'
+        return {'status_code': 200,
+                'content': '[{"language": "en", %s, '
+                             '"trace": [{"module": "module1", %s}]}]' %
+                             (c, c)}
+    else:
+        return {'status_code': 200,
+                'content': '[]'}
+
+class TestRecursion(PPPTestCase(app)):
+    def testRecursion(self):
+        self.config_file.write(config)
+        self.config_file.seek(0)
+        q = Request('1', 'en', Resource('one'), {}, [])
+        with HTTMock(my_module_mock, my_module2_mock):
+            answers = self.request(q)
+            self.assertEqual(len(answers), 2, answers)
+            self.assertEqual(answers[0].tree, Resource('three'))
+            self.assertEqual(answers[1].tree, Resource('two'))