Scalability Testing, part of the battery of non-functional 
tests, is the testing of a software application for 
measuring its capability to scale up or scale out [1]- in 
terms of any of its non-functional capability - be it the 
user load supported, the number of transactions, the data 
volume etc.

g

Scalability testing is to determine whether your 
application scales for the workload growth. Suppose your 
company expects a six-fold load increase on your server in 
the next two months. You may need to increase the server 
performance to shorten the request processing time to 
better serve visitors. If your application is scalable, you 
can shorten this time by upgrading the server hardware, for 
example, you can increase the CPU frequency and add more 
RAM. Also, you can increase the request performance by 
changing the server software, for example, by replacing the 
text-file data storages with SQL Server databases. To find 
a better solution, first you can test hardware changes, 
then software changes and after that compare the results of 
the tests.