Test JSONSchema resolver (#3223)

closes #2722

I don't love the current structure. There is a number of improvements that can be made:

JsonSchemaResolver can be refactored to have the following signature:

def __init__(schemas: Mapping[str, any], refs: Mapping[str, any])
  # schemas are all json files in `schemas/`, refs are all json files in `schemas/shared/`
Then we can thoroughly test the resolving behavior in JsonSchemaResolver independently from the logic for where we actually load schemas from.

I was tempted to make this refactor now but I'd rather cover more ground with tests then revisit. I created an issue to track this: #3222

airbyte-cdk/python/.coveragerc

@@ -0,0 +1,4 @@
+[run]
+omit =
+    # omit the models package
+    airbyte_cdk/models/*

airbyte-cdk/python/unit_tests/base_python/test_schema_helpers.py

@@ -0,0 +1,96 @@
+# MIT License
+#
+# Copyright (c) 2020 Airbyte
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+
+import json
+import os
+import shutil
+import sys
+from collections import Mapping
+from pathlib import Path
+
+from airbyte_cdk.base_python.schema_helpers import ResourceSchemaLoader
+from pytest import fixture
+
+MODULE = sys.modules[__name__]
+MODULE_NAME = MODULE.__name__.split(".")[0]
+SCHEMAS_ROOT = "/".join(os.path.abspath(MODULE.__file__).split("/")[:-1]) / Path("schemas")
+
+
+# TODO (sherif) refactor ResourceSchemaLoader to completely separate the functionality for reading data from the package. See https://github.com/airbytehq/airbyte/issues/3222
+#  and the functionality for resolving schemas. See https://github.com/airbytehq/airbyte/issues/3222
+@fixture(autouse=True, scope="session")
+def create_and_teardown_schemas_dir():
+    os.mkdir(SCHEMAS_ROOT)
+    os.mkdir(SCHEMAS_ROOT / "shared")
+    yield
+    shutil.rmtree(SCHEMAS_ROOT)
+
+
+def create_schema(name: str, content: Mapping):
+    with open(SCHEMAS_ROOT / f"{name}.json", "w") as f:
+        f.write(json.dumps(content))
+
+
+class TestResourceSchemaLoader:
+    # Test that a simple schema is loaded correctly
+    @staticmethod
+    def test_inline_schema_resolves():
+        expected_schema = {
+            "type": ["null", "object"],
+            "properties": {
+                "str": {"type": "string"},
+                "int": {"type": "integer"},
+                "obj": {"type": ["null", "object"], "properties": {"k1": {"type": "string"}}},
+            },
+        }
+
+        create_schema("simple_schema", expected_schema)
+        resolver = ResourceSchemaLoader(MODULE_NAME)
+        actual_schema = resolver.get_schema("simple_schema")
+        assert actual_schema == expected_schema
+
+    @staticmethod
+    def test_shared_schemas_resolves():
+        expected_schema = {
+            "type": ["null", "object"],
+            "properties": {
+                "str": {"type": "string"},
+                "int": {"type": "integer"},
+                "obj": {"type": ["null", "object"], "properties": {"k1": {"type": "string"}}},
+            },
+        }
+
+        partial_schema = {
+            "type": ["null", "object"],
+            "properties": {"str": {"type": "string"}, "int": {"type": "integer"}, "obj": {"$ref": "shared_schema.json"}},
+        }
+
+        referenced_schema = {"type": ["null", "object"], "properties": {"k1": {"type": "string"}}}
+
+        create_schema("complex_schema", partial_schema)
+        create_schema("shared/shared_schema", referenced_schema)
+
+        resolver = ResourceSchemaLoader(MODULE_NAME)
+
+        actual_schema = resolver.get_schema("complex_schema")
+        assert actual_schema == expected_schema