Mock Duplex implementation

MockDuplex.ts

class MockResponse extends Duplex {
    private chunks = Buffer.alloc(0);
    _write(chunk: Buffer, encoding: string, cb: Function) {
        this.chunks = Buffer.concat([this.chunks, chunk]);
        cb();
    }

    _read(size: number) {
        let result = true;
        while (result && this.chunks.length > 0) {
            const end = size > this.chunks.length ? this.chunks.length : size;
            const chunk = this.chunks.slice(0, end);
            this.chunks = this.chunks.slice(end, this.chunks.length);
            result = this.push(chunk);
        }
    }
}