a postman script to calculate the response time average and standard deviation of a request

postman-response-time-metrics.js

function standardDeviation(values, avg) {
    var squareDiffs = values.map(value => Math.pow(value - avg, 2));
    return Math.sqrt(average(squareDiffs));
}

function average(data) {
    return data.reduce((sum, value)=>sum + value) / data.length;
}

if (responseCode.code === 200 || responseCode.code === 201) {
    response_array = globals['response_times'] ? JSON.parse(globals['response_times']) : []
    response_array.push(responseTime)
    postman.setGlobalVariable("response_times", JSON.stringify(response_array))

    response_average = average(response_array);
    postman.setGlobalVariable('response_average', response_average)

    response_std = standardDeviation(response_array, response_average)
    postman.setGlobalVariable('response_std', response_std)
}

Hey @romcaname ,

I'm new to postman tests, how would I go about using this with pm.test?

Thanks!

Hey @romcaname

I am also wondering how to implement this.

Thanks, -Paul

Hey guys, Postman has a Pre-request Script and Tests tab with each request.

Unfortunately, "Tests" is, imho, very poorly named. It should have been named Post-request Script.

That being said, if you copy the above javascript into the "Tests" tab of the request you're benchmarking, you can find the data in your global variables.

I personally used this in conjunction with the ability postman gives you to run x number of iterations to get some stats on a certain request. Essentially, I put the request in its own collection, and then ran that collection 100 times. Just be sure to have the "keep variables" or "persist variables" option checked.

@electr0sheep has it right. This is how I've made use of the script.

Thank you for your detailed explanation!

I don't think this is needed anymore when you export the results of your test runner it gives you the average response time and the milliseconds of each request

@p0onage hmm when I export results I don't see the average response time. I see a list of response times in the times field, but I only see the latest run stored in the time field. I'm using postman v7.28.0.

{
	"id": "1a46165d-e0b7-4379-951f-6da25ce99662",
	"name": "Create Token",
	"time": 73,
	"responseCode": {
		"code": 401,
		"name": "Unauthorized"
	},
	"tests": {},
	"testPassFailCounts": {},
	"times": [
		189,
		73,
		73
	],
	"allTests": [
		{},
		{},
		{}
	]
},

If the average is available in the exported results, then I think this script could still be useful for those wanting to understand distribution of their response times via the standard deviation.

The export contains the total time so you can easily just divide that by number of requests. This is using Postman 7.33.1.

	"totalTime": 18630,
	"collection": {
		"requests": [
			{
				"id": "1d67e71f-dbf3-46de-9b7a-fd566d1ba59d",
				"method": "GET"
			}
		]
	}

Because of some deprecated code parts here is the code for the main part of the script for current Postman version (7.36.1):

if (pm.response.code === 200 || pm.response.code === 201) {
    response_array = pm.globals.get('response_times') ? JSON.parse(pm.globals('response_times')) : []
    response_array.push(pm.response.responseTime)
    pm.globals.set("response_times", JSON.stringify(response_array))

    response_average = average(response_array);
    pm.globals.set('response_average', response_average)

    response_std = standardDeviation(response_array, response_average)
    pm.globals.set('response_std', response_std)
}

When you want to use collection variables, use pm.collectionVariables instead of pm.globals. For environment variables use pm.environment.