Improve test fixtures

tests/helpers/sse-stream.ts

@@ -41,8 +41,6 @@ export class SseTestStream {
                       await new Promise((resolve) => setTimeout(resolve, chunkDelayMs));
                   }
 
-                  if (this.closed) return;
-
                   controller.enqueue(encoder.encode(chunks[i]!));
               }
 
@@ -57,8 +55,6 @@ export class SseTestStream {
    * Ends the HTTP body the way a server closing the SSE connection would.
    */
   close(): void {
-      if (this.closed) return;
-
       this.closed = true;
       this.controller?.close();
   }