There’s some preamble here. Jump to solution

Recently, I’ve been working on a client project that needs to function offline. This means that I have a subset of tests where I need to change the connectivity status of the browser driving the tests to simulate being offline to make assertions that the application is behaving correctly.

I already knew that the devtools had the capability to simulate either being completely offline, or to impose latency and throughput on the connection to simulate poor connectivity and/or older connection standards like 2G.

Because of this, I suspected that there would be an API to change the network connection status, I just had to track it down. After a bit of a journey through Selenium’s different layers (and languages - often I’m stumble across what I’m looking for in a different language binding for Selenium like .NET or Python, and then have to go and find the equivalent bit of code in Ruby), I found the solution:

#
# Sets network conditions
#
# @param [Hash] conditions
# @option conditions [Integer] :latency
# @option conditions [Integer] :throughput
# @option conditions [Boolean] :offline
#

def network_conditions=(conditions)
  @bridge.network_conditions = conditions
end

— Source

This method calls the setter on @bridge, which invokes the command through chromedriver to actually set the conditions:

# File 'selenium/webdriver/chrome/bridge.rb', line 45

def network_conditions=(conditions)
  execute :set_network_conditions, {}, {network_conditions: conditions}
end

This method is defined as an ‘extension’ (basically, a module) on the Capybara page’s driver’s browser (this is essentially a pointer to the running browser application). It functions as a setter method in Ruby, so we can just pass a hash to set the variables we want. It’s worth pointing out that I did have to provide all of these hash keys - it doesn’t appear to be possible to provide just one.

Here’s how I set my test browser to offline:

page.driver.browser.network_conditions = { offline: true, latency: 0, throughput: 0 }

And online again:

page.driver.browser.network_conditions = { offline: false, latency: 0, throughput: 0 }

You could also adjust latency and throughput if you wished, so while the application was technically online, it perhaps had very high latecy and very low throughput. This would be useful for testing some kind of ‘slow network connection’ message, for example.