text.createBufferSource();
            bufferSource.buffer = toneBuffer;

            let delay = context.createDelay();

            // Schedule delay time at time zero.
            delay.delayTime.setValueAtTime(delayTimeSeconds, 0);

            bufferSource.connect(delay);
            delay.connect(context.destination);
            bufferSource.start(0);

            context.startRendering()
                .then(buffer => checkDelayedResult(buffer, toneBuffer, should))
                .then(() => task.