Update and improve documentation on tests

[Darylgolden]

Enhancement proposal

Our documentation on tests is slightly outdated (it does not mention graphical unit tests for video). In addition, the phrasing and grammar are awkward at many places and could do with a copyedit.

Additional comments

[joybh98]

hey @Darylgolden , can I take up this issue ?

[Darylgolden]

Sure, go ahead!