test: add unit and integration test suite for the new SDK

- 268 unit tests covering all sync and async client methods
- 196 integration tests against a real sandbox API
- Mock-based tests using respx for sync and async HTTP mocking
- Paging, error handling, and edge case coverage (400/401/403/404/500/418)
- Integration test utilities and test data files
- .env.example with sandbox environment variables

tests/integration/utils/add_record.py

@@ -0,0 +1,33 @@
+import os
+
+import pytest
+
+from onspring_api_sdk import OnspringClient
+from onspring_api_sdk.models import Record, StringFieldValue
+
+
+def add_record(base_url: str, api_key: str) -> int:
+    client = OnspringClient(base_url, api_key)
+
+    survey_id = os.environ.get("TEST_SURVEY_ID")
+    text_field = os.environ.get("TEST_TEXT_FIELD")
+
+    if survey_id is None:
+        pytest.fail("TEST_SURVEY_ID is not defined")
+    if text_field is None:
+        pytest.fail("TEST_TEXT_FIELD is not defined")
+
+    app_id = int(survey_id)
+    field_id = int(text_field)
+
+    record = Record(
+        app_id=app_id,
+        fields=[StringFieldValue(field_id=field_id, value="test")],
+    )
+
+    response = client.add_or_update_record(record)
+
+    if response.data is None or response.data.id is None:
+        pytest.fail("Record ID is not defined")
+
+    return response.data.id