This is my code:

import { exec } from "child_process";

const hello = 'hello';
const goodbye = 'goodbye';

describe("nodejs exec write", () => {
  it("should run child process and write back to the stream", async () => {
    const execute = exec(`echo ${hello}`);
    execute.stdout?.on("readable", () => {
      console.log("on readable"); 
      execute.stdin?.write(`${goodbye}n`); 
      // write EPIPE
      //  > 17 |  execute.stdin?.write(`${goodbye}n`); 
    });
    const arrData: string[] = [];
    await new Promise((resolve, reject) => {
      console.log("on write");
      execute.stdout?.on("data", (data: any, x: any, y: any) => {
        arrData.push(data);
      });
      execute.stdout?.on("error", (err) => {
        console.log("error=", err);
        reject(err);
      });
      execute.stdout?.on("end", () => {
        resolve(true);
      });
    });

    expect(arrData).toEqual(expect.arrayContaining([hello, goodbye]));
  });
});

This returns error:
// write EPIPE
// > 11 | execute.stdin?.write(${goodbye}n);

What is the right way to write back to the stream?