Add integration test for non-nullable files

Existing integration tests for the file uploads plugin did not test for
non-nullable uploads. As this is realistically the more common case,
this commit adds a test to ensure that non-nullable files work as
expected.

This is necessary since the router does some substitution of the
variables for the file upload case which might cause validation issues
if not carefully tested.

Fixes #4708

apollo-router/tests/fixtures/file_upload/schema.graphql

@@ -82,6 +82,7 @@ type Mutation
   @join__type(graph: UPLOADS_CLONE)
 {
   singleUpload(file: Upload): File @join__field(graph: UPLOADS)
+  singleUploadNonNull(file: Upload!): File! @join__field(graph: UPLOADS)
   singleUploadClone(file: UploadClone): FileClone @join__field(graph: UPLOADS_CLONE)
   multiUpload(files: [Upload!]!): [File!]! @join__field(graph: UPLOADS)
   nestedUpload(nested: NestedUpload): File @join__field(graph: UPLOADS)

apollo-router/tests/integration/file_upload.rs

@@ -373,6 +373,59 @@ async fn it_supports_compression() -> Result<(), BoxError> {
         .await
 }
 
+#[tokio::test(flavor = "multi_thread")]
+async fn it_supports_non_nullable_file() -> Result<(), BoxError> {
+    use reqwest::multipart::Form;
+    use reqwest::multipart::Part;
+
+    // Construct a manual request for non nullable checks
+    let request = Form::new()
+        .part(
+            "operations",
+            Part::text(
+                serde_json::json!({
+                    "query": "mutation SomeMutation($file0: Upload!) {
+                        file0: singleUploadNonNull(file: $file0) { filename body }
+                    }",
+                    "variables": {
+                        "file0": null,
+                    },
+                })
+                .to_string(),
+            ),
+        )
+        .part(
+            "map",
+            Part::text(
+                serde_json::json!({
+                    "0": ["variables.file0"],
+                })
+                .to_string(),
+            ),
+        )
+        .part("0", Part::text("file0 contents").file_name("file0"));
+
+    helper::FileUploadTestServer::builder()
+        .config(FILE_CONFIG)
+        .handler(make_handler!(helper::echo_single_file))
+        .request(request)
+        .subgraph_mapping("uploads", "/")
+        .build()
+        .run_test(|request| {
+            insta::assert_json_snapshot!(request, @r###"
+            {
+              "data": {
+                "file0": {
+                  "filename": "file0",
+                  "body": "file0 contents"
+                }
+              }
+            }
+            "###);
+        })
+        .await
+}
+
 #[tokio::test(flavor = "multi_thread")]
 async fn it_supports_nested_file() -> Result<(), BoxError> {
     use reqwest::multipart::Form;