New API: add root use case in couple of tests

Add a use case for the root class to be tested in test_generic_read
and test_read_write_read_compare tests in test_apy.py

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

tests/test_api.py

@@ -33,6 +33,7 @@ def setUpModule():
  import tuf.exceptions
  from tuf.api.metadata import (
  Metadata,
+ Root,
  Snapshot,
  Timestamp,
  Targets
@@ -92,6 +93,7 @@ def tearDownClass(cls):
 
  def test_generic_read(self):
  for metadata, inner_metadata_cls in [
+ ('root', Root),
  ('snapshot', Snapshot),
  ('timestamp', Timestamp),
  ('targets', Targets)]:
@@ -137,7 +139,7 @@ def test_compact_json(self):
 
 
  def test_read_write_read_compare(self):
- for metadata in ['snapshot', 'timestamp', 'targets']:
+ for metadata in ['root', 'snapshot', 'timestamp', 'targets']:
  path = os.path.join(self.repo_dir, 'metadata', metadata + '.json')
  metadata_obj = Metadata.from_json_file(path)