replaced unclear list/map construct with a simpler for loop

Performed some supporting unit test improvements.

UnrealSoundsExtract.py

@@ -65,7 +65,8 @@ def DoExtraction(input, output, flatten):
                 filename,
                 os.path.join(os.path.abspath(output), ''))
             for filename in filenames]
-        list(map(os.system, commands))
+        for command in commands:
+            os.system(command)
     else:
         raise OSError(
             'No Files to Extract from in: {0}.'.format(repr(soundsDirectory)))

tests/test_UnrealSoundsExtract.py

@@ -1,6 +1,7 @@
 #!/usr/bin/python
 
 import unittest
+from unittest.mock import patch
 import os.path
 
 import UnrealSoundsExtract as ute
@@ -25,3 +26,27 @@ def test_no_sub_folder(self):
         actual = self.givenExtractorFilepath + \
             ' batchexport {0} sound wav "{1}"'
         self.assertEqual(given, actual)
+
+@patch('os.system', return_value=None)
+@patch('UnrealSoundsExtract.GetFilenamesInDirectory', return_value=[])
+class TestDoExtraction(unittest.TestCase):
+    def setUp(self):
+        self.given_input = os.path.join('.')
+        self.given_output = os.path.join('.', 'SoundsInWav')
+        self.given_flatten = False
+        self.expected_sounds_directory = os.path.join(self.given_input, 'Sounds')
+
+    def test_no_files(self, mock_get_filenames_in_directory, mock_os_system):
+        with self.assertRaisesRegex(OSError, r'^No Files to Extract from in:'):
+            ute.DoExtraction(self.given_input, self.given_output, self.given_flatten)
+        mock_get_filenames_in_directory.assert_called_with(self.expected_sounds_directory)
+        mock_os_system.assert_not_called()
+
+    def test_multiple_files(self, mock_get_filenames_in_directory, mock_os_system):
+        mock_get_filenames_in_directory.return_value = [
+            os.path.join(self.expected_sounds_directory, 'abc.uax'),
+            os.path.join(self.expected_sounds_directory, 'xyz.uax'),
+        ]
+        self.assertIsNone(ute.DoExtraction(self.given_input, self.given_output, self.given_flatten))
+        mock_get_filenames_in_directory.assert_called_with(self.expected_sounds_directory)
+        self.assertEqual(mock_os_system.call_count, 2)