timezone conversion: more unit tests

and code reorganization

common/lib/xmodule/xmodule/fields.py

@@ -19,6 +19,23 @@ class Date(ModelType):
     CURRENT_YEAR = datetime.datetime.now(UTC).year
     DEFAULT_DATE0 = datetime.datetime(CURRENT_YEAR, 1, 1, tzinfo=UTC)
     DEFAULT_DATE1 = datetime.datetime(CURRENT_YEAR, 2, 2, tzinfo=UTC)
+    def _parse_date_wo_default_month_day(self, field):
+        """
+        Parse the field as an iso string but prevent dateutils from defaulting the day or month while
+        allowing it to default the other fields.
+        """
+        # It's not trivial to replace dateutil b/c parsing timezones as Z, +03:30, -400 is hard in python
+        # however, we don't want dateutil to default the month or day (but some tests at least expect
+        # us to default year); so, we'll see if dateutil uses the defaults for these the hard way
+        result = dateutil.parser.parse(field, default=self.DEFAULT_DATE0)
+        result_other = dateutil.parser.parse(field, default=self.DEFAULT_DATE1)
+        if result != result_other:
+            log.warning("Field {0} is missing month or day".format(self._name, field))
+            return None
+        if result.tzinfo is None:
+            result = result.replace(tzinfo=UTC)
+        return result
+
     def from_json(self, field):
         """
         Parse an optional metadata key containing a time: if present, complain
@@ -30,17 +47,7 @@ class Date(ModelType):
         elif field is "":
             return None
         elif isinstance(field, basestring):
-            # It's not trivial to replace dateutil b/c parsing timezones as Z, +03:30, -400 is hard in python
-            # however, we don't want dateutil to default the month or day (but some tests at least expect
-            # us to default year); so, we'll see if dateutil uses the defaults for these the hard way
-            result = dateutil.parser.parse(field, default=self.DEFAULT_DATE0)
-            result_other = dateutil.parser.parse(field, default=self.DEFAULT_DATE1)
-            if result != result_other:
-                log.warning("Field {0} is missing month or day".format(self._name, field))
-                return None
-            if result.tzinfo is None:
-                result = result.replace(tzinfo=UTC)
-            return result
+            return self._parse_date_wo_default_month_day(field)
         elif isinstance(field, (int, long, float)):
             return datetime.datetime.fromtimestamp(field / 1000, UTC)
         elif isinstance(field, time.struct_time):