update tests based on code review

Author: bmoscon

tests/unit/date/test_util.py

@@ -101,7 +101,7 @@ def test_daterange_eq():
 
 def test_daterange_lt():
     dr = DateRange(dt(2013, 1, 1))
-    dr2 = DateRange(2001, 1, 1)
+    dr2 = DateRange(dt(2001, 1, 1))
 
     assert(dr2 < dr)
     dr.start = None

tests/unit/store/test_version_store_audit.py

@@ -9,9 +9,9 @@
 
 
 def test_data_change():
-    d = DataChange("a", "b")
-    assert(d.date_range == "a")
-    assert(d.new_data == "b")
+    d = DataChange(sentinel, sentinel)
+    assert(d.date_range == sentinel)
+    assert(d.new_data == sentinel)
 
 
 def test_ArcticTransaction_simple():