Made the "name" argument of track_screen_view optional

- fixes snowplow#103

Author: fblundun

CHANGES.txt

@@ -7,6 +7,7 @@ Stopped setting and sending tid (#94)
 Started setting and sending eid (#93)
 Allowed a single Tracker instance to send events to multiple Emitters (#91)
 Started passing a list of dictionaries to the on_failure callback for POST requests (#104)
+Made the "name" argument of track_screen_view optional (#103)
 
 Version 0.4.0 (2014-06-10)
 --------------------------

snowplow_tracker/test/integration/test_integration.py

@@ -110,12 +110,23 @@ def test_integration_ecommerce_transaction(self):
         self.assertEquals(from_querystring("dtm", querystrings[-3]), from_querystring("dtm", querystrings[-2]))
 
     def test_integration_screen_view(self):
-        t = tracker.Tracker([default_emitter], default_subject)
+        t = tracker.Tracker([default_emitter], default_subject, encode_base64=False)
         with HTTMock(pass_response_content):
-            t.track_screen_view("Game HUD 2", "Hello!")
+            t.track_screen_view("Game HUD 2", id_="534")
         expected_fields = {"e": "ue"}
         for key in expected_fields:          
             self.assertEquals(from_querystring(key, querystrings[-1]), expected_fields[key])
+        envelope_string = from_querystring("ue_pr", querystrings[-1])
+        envelope = json.loads(unquote_plus(envelope_string))
+        self.assertEquals(envelope, {
+            "schema": "iglu:com.snowplowanalytics.snowplow/unstruct_event/jsonschema/1-0-0",
+            "data": {"schema": "iglu:com.snowplowanalytics.snowplow/screen_view/jsonschema/1-0-0",
+                "data": {
+                    "name": "Game HUD 2",
+                    "id": "534"
+                }
+            }
+        })
 
     def test_integration_struct_event(self):
         t = tracker.Tracker([default_emitter], default_subject)

snowplow_tracker/test/unit/test_payload.py

@@ -21,7 +21,6 @@
 
 
 import unittest
-import time
 from snowplow_tracker import payload
 
 

snowplow_tracker/tracker.py

@@ -279,17 +279,19 @@ def track_ecommerce_transaction(self, order_id, total_value,
             return self
 
     @contract
-    def track_screen_view(self, name, id_=None, context=None, tstamp=None):
+    def track_screen_view(self, name=None, id_=None, context=None, tstamp=None):
         """
             :param  name:           The name of the screen view event
-            :type   name:           non_empty_string
+            :type   name:           string_or_none
             :param  id_:            Screen view ID
             :type   id_:            string_or_none
             :param  context:        Custom context for the event
             :type   context:        list(dict(string:*)) | None
             :rtype:                 tracker | list(int)
         """
-        screen_view_properties = {"name": name}
+        screen_view_properties = {}
+        if name is not None:
+            screen_view_properties["name"] = name        
         if id_ is not None:
             screen_view_properties["id"] = id_