Add the check for failed adding a path, because of path uniqueness.

features/path.feature

@@ -5,3 +5,8 @@ Feature: Adding an unique path
     When I add the path to the database
     Then the path should be added successfully
 
+  Scenario: Adding an new path with not uniq path
+    Given a path "/media"
+    When I add the path to the database
+    Then the exception should occur
+

features/steps/path_steps.py

@@ -22,3 +22,7 @@ def path_has_added(context):
     assert context.path.path == context.path_str
     assert context.exception_raised == False
 
+@then('the exception should occur')
+def path_has_not_added(context):
+    assert context.exception_raised == True
+