How to test a Lithium-Ion charging IC?
Your measurements may not be incorrect. 100 mA is a magic number for USB :)

From the datasheet, page 20:


  The USB input current limit setting 
  resets to 100mA when power is removed from its respective input. The WALL input current limit setting resets to 100mA when power is removed from both the USB and WALL inputs. 


Regardless of the 100 mA setting, I've always found it avoids unexpected problems to test the current with an actual battery installed. I have a short USB cable where I have removed an inch of the shielding from the middle and cut the power wire. I then connect a current meter to each end of that wire.

I realize that this doesn't answer your question about battery simulation, but I hope it helps!