Add tests for negative values.

test/FilterTest.py

@@ -286,6 +286,16 @@ class FilterTest(unittest.TestCase):
         self.assertEquals(todolist_to_string(filtered_todos),
             todolist_to_string(reference))
 
+    def test_filter30(self):
+        todos = load_file('data/FilterTest3.txt')
+        otf = Filter.OrdinalTagFilter('value:>-8')
+
+        filtered_todos = otf.filter(todos)
+        reference = load_file('data/FilterTest13-result.txt')
+
+        self.assertEquals(todolist_to_string(filtered_todos),
+            todolist_to_string(reference))
+
 class OrdinalTagFilterTest(unittest.TestCase):
     def setUp(self):
         today = date.today()

test/data/FilterTest10-result.txt

 Tag with some value:8
+Tag with negative value:-7

test/data/FilterTest13-result.txt

+Tag with some value:8
+Tag with some other value:16
+Tag with negative value:-7

test/data/FilterTest3.txt

@@ -3,3 +3,4 @@ Tag with future due date due:2030-01-01
 Tag with some value:8
 Tag with some other value:16
 Tag with nonsense value:nonsense
+Tag with negative value:-7

test/data/FilterTest8-result.txt

 Tag with some value:8
+Tag with negative value:-7

test/data/FilterTest9-result.txt

 Tag with some value:8
 Tag with some other value:16
+Tag with negative value:-7