In i.MXRT1050 SDK we released, we provide examples code for each interface, whose purpose is to help customer understand how to use these interfaces.
Except these examples ,we don't have others for you. Actually they are enough for you. If you want to use other UARTs, you can add them to the example for test purpose.
For example, you can let the example supports UART2 and UART3, then test transmission between these 2 UARTs. Or you can install COM test tool on windows PC(or Linux Host), testing communications between RT1050 board and PC.
Hope these information is helpful for you!
Have a nice day!