Mocha capture stdout

capture_stream.ts

import { WriteStream } from 'tty';

type callback = (error: Error | null | undefined) => void;
export interface Capture {
    unhook: () => void;
    captured: () => string;
}

export const captureStream = (stream: WriteStream): Capture => {
    const oldWrite = stream.write;
    let output = '';
    stream.write = (chunk: unknown, encoding: string | callback, cb?: callback): boolean => {
        output += chunk.toString(); // chunk is a String or Buffer
        return oldWrite.apply(stream, cb ? [chunk, encoding, cb] : [chunk, encoding, cb]);
    }

    return {
        unhook: (): void => {
            stream.write = oldWrite;
        },
        captured: (): string => {
            return output;
        }
    };
}