test: share streaming error response helper

extensions/test-support/streaming-error-response.ts

@@ -0,0 +1,22 @@
+export function createStreamingErrorResponse(params: {
+  status: number;
+  chunkCount: number;
+  chunkSize: number;
+  byte: number;
+}): { response: Response; getReadCount: () => number } {
+  let reads = 0;
+  const stream = new ReadableStream<Uint8Array>({
+    pull(controller) {
+      if (reads >= params.chunkCount) {
+        controller.close();
+        return;
+      }
+      reads += 1;
+      controller.enqueue(new Uint8Array(params.chunkSize).fill(params.byte));
+    },
+  });
+  return {
+    response: new Response(stream, { status: params.status }),
+    getReadCount: () => reads,
+  };
+}