If you want to test how long a file could take to transfer but do not have a test file the exact size you can create one to fit your need case. 

Start by opening a command prompt as administrator and then enter the follwowing command:

fsutil file createnew <filename> <length>

For my example I am going to create a file in C:\temp which is 2Gb in size

Notice that I have entered the value of what 2 Gibibytes would be not 2 Gigabytes as windows will create this using binary and not metric. 

This is a method you can use to create a test file of any size. The name of the file and extention can be anything as it is filled with null data and will still take up the same block value on disk.