✨ Add ResponseValidationError printable details, to show up in serv…

…er error logs (#10078)

fastapi/exceptions.py

@@ -47,3 +47,9 @@ class ResponseValidationError(ValidationException):
     def __init__(self, errors: Sequence[Any], *, body: Any = None) -> None:
         super().__init__(errors)
         self.body = body
+
+    def __str__(self) -> str:
+        message = f"{len(self._errors)} validation errors:\n"
+        for err in self._errors:
+            message += f"  {err}\n"
+        return message

tests/test_response_model_as_return_annotation.py

@@ -277,13 +277,15 @@ def test_response_model_no_annotation_return_exact_dict():
 
 
 def test_response_model_no_annotation_return_invalid_dict():
-    with pytest.raises(ResponseValidationError):
+    with pytest.raises(ResponseValidationError) as excinfo:
         client.get("/response_model-no_annotation-return_invalid_dict")
+    assert "missing" in str(excinfo.value)
 
 
 def test_response_model_no_annotation_return_invalid_model():
-    with pytest.raises(ResponseValidationError):
+    with pytest.raises(ResponseValidationError) as excinfo:
         client.get("/response_model-no_annotation-return_invalid_model")
+    assert "missing" in str(excinfo.value)
 
 
 def test_response_model_no_annotation_return_dict_with_extra_data():
@@ -313,13 +315,15 @@ def test_no_response_model_annotation_return_exact_dict():
 
 
 def test_no_response_model_annotation_return_invalid_dict():
-    with pytest.raises(ResponseValidationError):
+    with pytest.raises(ResponseValidationError) as excinfo:
         client.get("/no_response_model-annotation-return_invalid_dict")
+    assert "missing" in str(excinfo.value)
 
 
 def test_no_response_model_annotation_return_invalid_model():
-    with pytest.raises(ResponseValidationError):
+    with pytest.raises(ResponseValidationError) as excinfo:
         client.get("/no_response_model-annotation-return_invalid_model")
+    assert "missing" in str(excinfo.value)
 
 
 def test_no_response_model_annotation_return_dict_with_extra_data():
@@ -395,13 +399,15 @@ def test_response_model_model1_annotation_model2_return_exact_dict():
 
 
 def test_response_model_model1_annotation_model2_return_invalid_dict():
-    with pytest.raises(ResponseValidationError):
+    with pytest.raises(ResponseValidationError) as excinfo:
         client.get("/response_model_model1-annotation_model2-return_invalid_dict")
+    assert "missing" in str(excinfo.value)
 
 
 def test_response_model_model1_annotation_model2_return_invalid_model():
-    with pytest.raises(ResponseValidationError):
+    with pytest.raises(ResponseValidationError) as excinfo:
         client.get("/response_model_model1-annotation_model2-return_invalid_model")
+    assert "missing" in str(excinfo.value)
 
 
 def test_response_model_model1_annotation_model2_return_dict_with_extra_data():