I'm assuming 'our FTP' is your Enhanced FTP provided with your Salesforce Marketing Cloud account?
If so, you can do what I think you're trying to achieve in a number of ways. Firstly, if you're just wanting to manually run an Import Activity or you're running it in a scheduled automation, you can use personalization strings to substitute the date variables in your file name. For example, you can pick up today's file with a file name in your import activity accordingly:
test_%%Year%%%%Month%%%%Day%%.csv
You can also restrict files considered by altering the system buffer in the advanced settings of the Import Activity. This allows you to only consider files created within a given time period, irrespective of file name.
Depending on your use case, you should also consider using a File Drop Automation. These are started immediately on arrival a new file and more often fit the purpose of processing inbound files. You can pass the name of the newly arrived file into your Import Activity using Substitution Strings. For example, the following used for the file name in your Import Activity would automatically use the name of the newly arrived file:
%%FILENAME_FROM_TRIGGER%%