Add and update tests for _check_path() method

- add a test for _check_path() method of Targets class.
- update all tests calling _check_path() respectively
- update test_tutorial

Signed-off-by: Teodora Sechkova <[email protected]>

Author: sechkova

tests/test_mix_and_match_attack.py

@@ -218,7 +218,7 @@ def test_with_tuf(self):
     # new version is generated.
     with open(file3_path, 'wt') as file_object:
       file_object.write('This is role2\'s target file.')
-    repository.targets('role1').add_target(file3_path)
+    repository.targets('role1').add_target(os.path.basename(file3_path))
 
     repository.writeall()