Handle ImportError for optional JSON response imports

fastapi/responses.py

@@ -26,13 +26,13 @@ class _OrjsonModule(Protocol):
 
 try:
     ujson = cast(_UjsonModule, importlib.import_module("ujson"))
-except ModuleNotFoundError:  # pragma: nocover
+except ImportError:  # pragma: nocover
     ujson = None  # type: ignore[assignment]
 
 
 try:
     orjson = cast(_OrjsonModule, importlib.import_module("orjson"))
-except ModuleNotFoundError:  # pragma: nocover
+except ImportError:  # pragma: nocover
     orjson = None  # type: ignore[assignment]
 
 

tests/test_responses_import.py

@@ -0,0 +1,40 @@
+import subprocess
+import sys
+import textwrap
+from pathlib import Path
+
+import pytest
+
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+
+
+@pytest.mark.parametrize("optional_module_name", ("ujson", "orjson"))
+def test_responses_imports_when_optional_json_import_raises_import_error(
+    optional_module_name: str,
+) -> None:
+    code = textwrap.dedent(
+        f"""
+        import importlib
+
+        real_import_module = importlib.import_module
+
+        def fake_import_module(name, package=None):
+            if name == {optional_module_name!r}:
+                raise ImportError("simulated optional dependency load failure")
+            return real_import_module(name, package)
+
+        importlib.import_module = fake_import_module
+
+        import fastapi.responses as responses
+
+        assert getattr(responses, {optional_module_name!r}) is None
+        """
+    )
+    result = subprocess.run(
+        [sys.executable, "-c", code],
+        capture_output=True,
+        cwd=REPO_ROOT,
+        text=True,
+    )
+    assert result.returncode == 0, result.stderr + result.stdout