Fix incorrect exception for bad paths

fiasko_bro/repository_info.py

@@ -67,6 +67,8 @@ def is_tracked_directory(self, directory):
 class ProjectFolder:
 
     def __init__(self, path, directories_to_skip=None):
+        if not os.path.isdir(path):
+            raise FileNotFoundError('Path "{}" not found or is not a directory.'.format(path))
         self.path = path
         self._parsed_py_files = self._get_parsed_py_files(directories_to_skip)
         try:

tests/test_validation_interface/test_incorrect_input_handled.py

@@ -0,0 +1,17 @@
+import os.path
+
+import pytest
+
+from fiasko_bro import validate
+
+
+@pytest.fixture(scope='session')
+def non_existent_directory():
+    directory = 'test_fixtures{}directory_that_should_not_exist'.format(os.path.sep)
+    assert not os.path.isdir(directory)
+    return directory
+
+
+def test_not_existing_file_raises_correct_exception(non_existent_directory):
+    with pytest.raises(FileNotFoundError):
+        validate(non_existent_directory)