qmake: How do I copy .dll/.so's to the output directory?

Add this to your pro file:

target.path = ../testProject/$$TARGET
INSTALLS += target 

# Copy the dynamic library.
win32 {
   QMAKE_PRE_LINK=copy /Y lib\qextserialport\src\build\qextserialportd.dll debug\ & copy /Y lib\qextserialport\src\build\qextserialport.dll release\
}
else {
   # TODO: Unices
}

This works, for the QextSerialPort library. Supports Qt's debug_and_release mode.

QMAKE_POST_LINK also works, but will throw an error if you're trying to run the app immediately: then your .dll will be copied too late. QMAKE_PRE_LINK does copy it in time.

I use INSTALLS, like so. (qmake documentation)