feat: scanner provides list of extensions that are not on valid list

app/scanner.py

@@ -1,3 +1,4 @@
+from functools import partial
 import os
 
 VALID_PHOTO_EXTENSIONS = ['.bmp', '.gif', '.jpg', '.jpeg', '.png', '.tif', '.tiff']
@@ -7,10 +8,28 @@
 
 class Scanner:
 
-    def scan_directory(self, source_dir):
+    def valid_filepaths_in(self, source_dir):
+        return self.__scan_directory(source_dir, self.__ext_valid, self.__full_file_path)
+
+    def invalid_extensions_in(self, source_dir):
+        return set(self.__scan_directory(source_dir, self.__ext_invalid, self.__extension_only))
+
+    def __ext_valid(self, file):
+        return self.__extension(file) in VALID_EXTENSIONS
+
+    def __ext_invalid(self, file):
+        return self.__extension(file) not in VALID_EXTENSIONS
+
+    def __extension(self, file):
+        return os.path.splitext(file)[1]
+
+    def __full_file_path(self, root, file):
+        return os.path.join(root, file)
+
+    def __extension_only(self, _, file):
+        return self.__extension(file)
+
+    def __scan_directory(self, source_dir, extension_filter, path_constructor):
         file_tree = os.walk(source_dir)
         for (root, _, files) in file_tree:
-            for file in files:
-                _, extension = os.path.splitext(file)
-                if extension in VALID_EXTENSIONS:
-                    yield os.path.join(root, file)
+            yield from filter(extension_filter, map(partial(path_constructor, root), files))

test/test_scanner.py

@@ -13,7 +13,7 @@ def teardown():
 def test_scanner_discovers_files_to_be_copied():
     create_files_with_desired_extensions()
 
-    files_to_copy = scanner.scan_directory(source_directory)
+    files_to_copy = scanner.valid_filepaths_in(source_directory)
 
     assert sorted(list(files_to_copy)) == valid_source_filepaths()
 
@@ -22,7 +22,7 @@ def test_scanner_ignores_files_without_desired_extensions():
     create_files_with_desired_extensions()
     create_files_without_desired_extensions()
 
-    files_to_copy = scanner.scan_directory(source_directory)
+    files_to_copy = scanner.valid_filepaths_in(source_directory)
 
     assert sorted(list(files_to_copy)) == valid_source_filepaths()
 
@@ -31,6 +31,25 @@ def test_copies_file_when_provided_source_path_does_not_have_trailing_backslash(
     filename = 'a_file.jpeg'
     source_filepath = create_file(source_directory, filename)
     source_directory_without_trailing_backslash = source_directory[0:-1]
-    files_to_copy = scanner.scan_directory(source_directory_without_trailing_backslash)
+    files_to_copy = scanner.valid_filepaths_in(source_directory_without_trailing_backslash)
 
     assert list(files_to_copy) == [source_filepath]
+
+
+def test_provides_a_set_of_invalid_file_extensions():
+    create_file(source_directory, 'a_file.non')
+    create_file(source_directory, 'a_file_2.non')
+    result = scanner.invalid_extensions_in(source_directory)
+    extension = '.non'
+
+    assert list(result) == [extension]
+    assert len(list(result)) == 1
+
+
+def test_provides_multiple_invalid_extensions():
+    create_file(source_directory, 'a_file.non')
+    create_file(source_directory, 'a_file_2.hlp')
+    result = scanner.invalid_extensions_in(source_directory)
+    extensions = sorted(['.non', '.hlp'])
+
+    assert sorted(list(result)) == extensions