How to test javascript webhook?

My program currently makes requests to a server. I'm building a webhook that, when triggered, should send data to a different server. This second server isn't set up yet, so I'm trying to mock the response from this server. What are best tools and practices to execute my webhook in a production style environment?

For what it's worth, this is what the webhook looks like (using axios):

const webhookResult = await this.axiosInstance.post('/webhook/endpoint/not/yet/in/production', dataToSend, {
    headers: {
        'User-Id': userId
    },
});