Recently I came across an old DOS command that can help verify SharePoint maximum upload file size. FSUTIL enables us to create a file of any given size. For example, if your SharePoint farm has a maximum file upload of 200MB you can create a 195 MB and 205MB test file. Uploading both would validate when 195MB is successful and 205MB fails.
$x = 195MB
fsutil file createnew 195.txt $x
$x = 205MB
fsutil file createnew 205.txt $x