Add serializer for request validation

src/paper/serializers/paper_upload_serializer.py

@@ -0,0 +1,10 @@
+from rest_framework import serializers
+
+
+class PaperUploadSerializer(serializers.Serializer):
+    """
+    Serializer for uploading a paper.
+    Used to validate request data.
+    """
+
+    filename = serializers.CharField(required=True)

src/paper/tests/test_paper_upload_view.py

@@ -40,3 +40,17 @@ def test_post(self):
             "test.pdf",
             request.user.id,
         )
+
+    def test_post_fails_with_validation_error(self):
+        # Arrange
+        request = self.factory.post("/paper/upload/", {})
+
+        force_authenticate(request, self.user)
+
+        # Act
+        response = self.view(request, storage_service=self.mock_storage_service)
+
+        # Assert
+        self.assertEqual(response.status_code, 400)
+        self.assertEqual(response.data, {"filename": ["This field is required."]})
+        self.mock_storage_service.create_presigned_url.assert_not_called()

src/paper/views/paper_upload_views.py

@@ -3,6 +3,7 @@
 from rest_framework.response import Response
 from rest_framework.views import APIView
 
+from paper.serializers.paper_upload_serializer import PaperUploadSerializer
 from paper.services.storage_service import StorageService
 
 
@@ -24,6 +25,10 @@ def post(self, request: Request, *args, **kwargs) -> Response:
         user = request.user
         data = request.data
 
+        # Validate request data
+        serializer = PaperUploadSerializer(data=request.data)
+        serializer.is_valid(raise_exception=True)
+
         filename = data.get("filename")
 
         presigned_url = self.storage_service.create_presigned_url(filename, user.id)