YANG: tests: validate our sample data against the YANG model

I'm using the yagnson library for this, and that library needs two
pieces of data as its inputs:

- a "YANG Module Library", which is usually a JSON description of all
available and activated YANG modules along its enabled features, etc,

- actual YANG models, typically specified as a list of filesystem paths
which hold them.

I generated that ietf-yanglib file via something like:

 $ python path/to/yangson/tools/python/mkylib.py \
     gnpy/yang/ext \
     gnpy/yang/tip \
     > gnpy/yang/yanglib.json`

When this adds support for `ietf-geo-location` in future, make sure to
edit the output so that it does not accidentally enable all of the
geolocation features (but that's for later, anyway). And we might
actually not end up doing that.

Change-Id: I51e342cd556ecc381ff0bf35df2bfa70f5f83ba8

tests/test_yang_validation.py

@@ -6,11 +6,12 @@
 # see LICENSE.md for a list of contributors
 #
 
-from gnpy.yang import external_path, model_path
+from gnpy.yang import external_path, model_path, create_datamodel
 from pathlib import Path
 from typing import List
 import pytest
 import subprocess
+import json
 
 
 def _get_basename(filename: Path) -> str:
@@ -44,3 +45,18 @@ def _validate_yang_model(filename: Path, options: List[str]):
         stdout=subprocess.PIPE, stderr=subprocess.PIPE, check=True, universal_newlines=True)
     assert proc.stderr == ''
     assert proc.stdout == ''
+
+
+@pytest.fixture
+def _yangson_datamodel():
+    return create_datamodel
+
+
+@pytest.mark.parametrize("filename", (Path(__file__).parent / 'yang').glob('*.json'), ids=_get_basename)
+def test_validate_yang_data(_yangson_datamodel, filename: Path):
+    '''Validate a JSON file against our YANG models'''
+    dm = _yangson_datamodel()
+    with open(filename, 'r') as f:
+        raw_json = json.load(f)
+    data = dm.from_raw(raw_json)
+    data.validate()