Function start

packages/effect/test/Stream.test.ts:517–519

(controller)

          evaluate: () =>
            new ReadableStream<number>({
              start(controller) {
                controller.error(new Error("boom"))
              }
            }),
          onError: (error) => new Error(`mapped: ${(error as Error).message}`)
        }).pipe(Stream.runDrain, Effect.exit)