Here is a almost full Monty,
Adds SD test, RTC, and some BLE LED control rolled in. 
if you have a Mobile or Nrf connect for Desktop with a Nordic Dongle , Another $9 tool a must have.
Enjoy , Drag & Drop.
SelfTest_Xiao_Expansion.zip (264.3 KB)
This is the Serial output
Power ON
Xiao Expansion board and MCU check & Test compiled on Mar 23 2024 at 17:42:35
Processor came out of reset.
Selected MCU: nRF52840
Xiao Unit: EA52
Playing startup sound
RTC Date & Time is:3/19/24 10:17:21
Testing R G B LED - RED, GREEN, BLUE...
Initializing SD card...Card Mounted
Card type: SDHC
Volume type is: FAT32
SD Volume size (Gb): 29.12
Xiao MAC: BF:49:C1:6B:01:4D
Advertising Bluetooth Device
as: Xiao EA52
Connected to central: c8:65:29:7e:60:0c // this will pop in when you connect to it.
HTH
GL 
PJ 