Coding for the Load-test

There are a few considerations for creating a good load-test. Although load tests can and often should be built by reusing your assets that “talk to your app”, the actual code that “runs” should be implemented to follow certain guidelines when run for a load test.


In order to make load requests have realistic pacing, BrowserUp uses a “think_time” setting for each Profile (see here). The think_time setting, which represents the number of seconds to sleep between each step (in a browser a step might be a page load, in an API test, a Request, for example)

The think_time setting your profile is pushed into your code’s container when it runs your code as an environment variable.

Your test is responsible for implementing the code that sleeps. Typically, in pseudo code, this is something like:

  • Do something
  • sleep(ENV[‘THINK_TIME’])
  • Do something else
  • sleep(ENV[‘THINK_TIME’])
  • Do something
  • Loop

There are several reasons for using think time: 1 - It ensures that the load tests are consistent. If a load test runs full-bore, then today’s load test can’t be compared to tomorrows. For example, if your application’s speed is doubled, then the same test, run tomorrow, might make twice as many requests as it did today, while appearing to be bottlenecked on both days. Even worse, if the CPU or networking of the machines driving the load have differences, you’ll get inconsistent results.

Think time ensures that there is capacity to spare on the CPU of the load-generating machines.

2 - It ensures the machine has capacity to do other things, like send back metrics to the data collector.

For these reasons, your scripts should always implement think_time, and delay between iterations.

Think time is used between each “step.” DELAY_BETWEEN_ITERATIONS should be the last step in the script.


Most tests need to use varied data. BrowserUp provides Databanking for data driven tests.

With databanking set up, the current databank variable is made available to your container via environment variables.

To use them, your code needs to retrieve the current value from the environment. If your profile is set to be iterated by the system, it will retrieve a new value on each iteration.

If your code is set to iterate iteself (it loops) it will receive values on start, but that will be all.


There are two approaches to iterating:

  1. BrowserUp will call the command defined for your profile, and wait for it to finish for each iteration
  2. Your code loops (iterates) on it’s own.

If your artifact is code that runs once, and completes for each iteration, in your profile, set

iterate: true

If your code handles looping, is taking over the iteration responsibility, tell BrowserUp not to iterate it, with

iterate: false