Add tests/test_cdaweb_failures.py: failure-path unit test for CDA

Mocks speasy.data_providers.cda.http.get to return a 500 so the unit
tier verifies that a CDA server error surfaces as CdaWebException
rather than being silently swallowed.

Author: jeandet

tests/test_cdaweb_failures.py

@@ -0,0 +1,59 @@
+"""Failure-path tests for CDA using mocked HTTP responses.
+
+Cassette replay covers happy paths from real CDA responses. These
+tests cover failure paths cassettes cannot easily reach: server 5xx
+errors. They run on the unit tier because the HTTP behaviour is
+fully controlled by the mock (no network).
+"""
+
+from __future__ import annotations
+
+import unittest
+from datetime import datetime, timezone
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+import speasy as spz
+from speasy.data_providers.cda import CdaWebException
+
+pytestmark = pytest.mark.unit
+
+
+def _fake_http_response(status: int, body: bytes = b'{"Message": ["Internal error"]}') -> MagicMock:
+    """Build a minimal stand-in for the speasy ``Response`` returned by
+    ``speasy.core.http.get`` so the CDA wrapper sees a 5xx with a JSON
+    body it can parse."""
+    resp = MagicMock()
+    resp.status_code = status
+    resp.ok = False
+    resp.url = "https://cdaweb.gsfc.nasa.gov/WS/cdasr/1/fake"
+    resp.json.return_value = {"Message": ["Internal error"]}
+    resp.bytes = body
+    resp.text = body.decode()
+    return resp
+
+
+class CdaFailureModes(unittest.TestCase):
+
+    def test_get_variable_propagates_server_500(self) -> None:
+        """A 500 from CDA must surface as ``CdaWebException`` so callers can
+        distinguish a server error from a legitimate "no data" response."""
+        with patch(
+            "speasy.data_providers.cda.http.get",
+            return_value=_fake_http_response(500),
+        ):
+            with self.assertRaises(CdaWebException):
+                spz.cda.get_variable(
+                    dataset="THA_L2_FGM",
+                    variable="tha_fgl_gsm",
+                    start_time=datetime(2014, 6, 1, tzinfo=timezone.utc),
+                    stop_time=datetime(2014, 6, 1, 0, 5, tzinfo=timezone.utc),
+                    disable_proxy=True,
+                    disable_cache=True,
+                    method="API",
+                )
+
+
+if __name__ == "__main__":
+    unittest.main()