generator lib: Initial tests

Move existing tests into a new __tests__ module under generator/lib.
Also define a new test for `util.new_context`, to prevent regressions as
changes are made.

src/generator/lib/__tests__/test_data/discovery_document.py

@@ -1,3 +1,6 @@
+# Discovery document for photoslibrary, retrieved from:
+# https://photoslibrary.googleapis.com/$discovery/rest?version=v1
+DISCOVERY_DOC = r"""
 {
   "documentationLink": "https://developers.google.com/photos/",
   "id": "photoslibrary:v1",
@@ -1332,3 +1335,4 @@
   "kind": "discovery#restDescription",
   "basePath": ""
 }
+"""

src/generator/lib/__tests__/util_test.py

@@ -1,20 +1,12 @@
 #!/usr/bin/env python
 
-import importlib.resources
 import unittest
 import json
 
-from generator.lib.util import to_api_version, library_name, re_find_replacements, to_rust_type, new_context
-import generator.lib.test_data as test_data
+from generator.lib.util import to_api_version, library_name, re_find_replacements, to_rust_type
+from .test_data.discovery_document import DISCOVERY_DOC
 
 
-TEST_JSON_FILE = "photoslibrary-api.json"
-
-
-def read_test_json_file():
-    data = importlib.resources.read_text(test_data, TEST_JSON_FILE)
-    return json.loads(data)
-
 class UtilsTest(unittest.TestCase):
 
     def test_to_version_ok(self):
@@ -68,7 +60,7 @@ class UtilsTest(unittest.TestCase):
         self.assertEqual(ms[0], '{+project}')
 
     def test_to_rust_type(self):
-        full_api_schema = read_test_json_file()
+        full_api_schema = json.loads(DISCOVERY_DOC)
 
         schemas = full_api_schema['schemas']