Move tests to test_metadata_serialization

Move the Delegation class serialization tests from "test_api.py"
to test_metadata_serialization.py module focused on serialization
testing.

Additionally, a test for empty keys and roles will be added in my
upcomming pr theupdateframework#1511.

Signed-off-by: Martin Vrachev <mvrachev@vmware.com>

tests/test_api.py

@@ -510,23 +510,6 @@ def test_metadata_root(self):
  root.signed.remove_key('root', 'nosuchkey')
 
 
- def test_delegation_class(self):
- # empty keys and roles
- delegations_dict = {"keys":{}, "roles":[]}
- delegations = Delegations.from_dict(delegations_dict.copy())
- self.assertEqual(delegations_dict, delegations.to_dict())
-
- # Test some basic missing or broken input
- invalid_delegations_dicts = [
- {},
- {"keys":None, "roles":None},
- {"keys":{"foo":0}, "roles":[]},
- {"keys":{}, "roles":["foo"]},
- ]
- for d in invalid_delegations_dicts:
- with self.assertRaises((KeyError, AttributeError)):
- Delegations.from_dict(d)
-
  def test_metadata_targets(self):
  targets_path = os.path.join(
  self.repo_dir, 'metadata', 'targets.json')

tests/test_metadata_serialization.py

@@ -270,6 +270,11 @@ def test_invalid_delegated_role_serialization(self, test_case_data: str):
 
 
  invalid_delegations: DataSet = {
+ "empty delegations": '{}',
+ "bad keys": '{"keys": "foo", \
+ "roles": [{"keyids": ["keyid"], "name": "a", "paths": ["fn1", "fn2"], "terminating": false, "threshold": 3}]}',
+ "bad roles": '{"keys": {"keyid" : {"keytype": "rsa", "scheme": "rsassa-pss-sha256", "keyval": {"public": "foo"}}}, \
+ "roles": ["foo"]}',
  "duplicate role names": '{"keys": {"keyid" : {"keytype": "rsa", "scheme": "rsassa-pss-sha256", "keyval": {"public": "foo"}}}, \
  "roles": [ \
  {"keyids": ["keyid"], "name": "a", "paths": ["fn1", "fn2"], "terminating": false, "threshold": 3}, \
@@ -281,7 +286,7 @@ def test_invalid_delegated_role_serialization(self, test_case_data: str):
  @run_sub_tests_with_dataset(invalid_delegations)
  def test_invalid_delegation_serialization(self, test_case_data: str):
  case_dict = json.loads(test_case_data)
- with self.assertRaises(ValueError):
+ with self.assertRaises((ValueError, KeyError, AttributeError)):
  Delegations.from_dict(copy.deepcopy(case_dict))