When it comes to testing the speed of your shopify plus store development, 
there are several methods available. You can use Lighthouse, 
Pingdom, or PageSpeed Insight. You can also use the speed dashboard in 
Shopify. However, be aware that these methods are not as reliable as they should be.

If you want to increase the speed of your Shopify store, it’s 
important to know which resources are used by visitors. 
Some elements of your store are cached on the customer’s local 
storage, such as JS and CSS files. Others are cached on the server. 
You can also disable certain features in your store. This will result in a faster website.