Make get_duration return the proper type

The get_duration code was borrowed from tempest's subunit-trace script
which had it return a string marking it in secs. However, a float was
the proper type for the variable. So instead of converting the return
for every instance just have it return the proper type.

subunit2sql/read_subunit.py

@@ -22,12 +22,12 @@ DAY_SECONDS = 60 * 60 * 24
 
 def get_duration(start, end):
     if not start or not end:
-        duration = ''
+        duration = None
     else:
         delta = end - start
-        duration = '%d.%06ds' % (
+        duration = '%d.%06d' % (
             delta.days * DAY_SECONDS + delta.seconds, delta.microseconds)
-        return duration
+        return float(duration)
 
 
 class ReadSubunit(object):
@@ -112,6 +112,5 @@ class ReadSubunit(object):
     def run_time(self):
         runtime = 0.0
         for name, data in self.results.items():
-            runtime += float(get_duration(data['start_time'],
-                                          data['end_time']).strip('s'))
+            runtime += get_duration(data['start_time'], data['end_time'])
         return runtime

subunit2sql/shell.py

@@ -58,8 +58,8 @@ def parse_args(argv, default_config_files=None):
 def running_avg(test, values, result):
     count = test.success
     avg_prev = test.run_time
-    curr_runtime = float(subunit.get_duration(result['start_time'],
-                                              result['end_time']).strip('s'))
+    curr_runtime = subunit.get_duration(result['start_time'],
+                                        result['end_time'])
     if isinstance(avg_prev, float):
         # Using a smoothed moving avg to limit the affect of a single outlier
         new_avg = ((count * avg_prev) + curr_runtime) / (count + 1)
@@ -119,13 +119,8 @@ def process_results(results):
             else:
                 fails = 0
                 success = 0
-            run_time = subunit.get_duration(
-                results[test]['start_time'],
-                results[test]['end_time']).strip('s')
-            if run_time:
-                run_time = float(run_time)
-            else:
-                run_time = None
+            run_time = subunit.get_duration(results[test]['start_time'],
+                                            results[test]['end_time'])
             db_test = api.create_test(test, (success + fails), success,
                                       fails, run_time,
                                       session)

subunit2sql/tests/test_read_subunit.py

@@ -23,4 +23,14 @@ class TestReadSubunit(base.TestCase):
     def test_get_duration(self):
         dur = subunit.get_duration(datetime.datetime(1914, 6, 28, 10, 45, 0),
                                    datetime.datetime(1914, 6, 28, 10, 45, 50))
-        self.assertEqual(dur, '50.000000s')
+        self.assertEqual(dur, 50.000000)
+
+    def test_get_duration_no_start(self):
+        dur = subunit.get_duration(None,
+                                   datetime.datetime(1914, 6, 28, 10, 45, 50))
+        self.assertIsNone(dur)
+
+    def test_get_duration_no_end(self):
+        dur = subunit.get_duration(datetime.datetime(1914, 6, 28, 10, 45, 50),
+                                   None)
+        self.assertIsNone(dur)