I'm new on Raspberry Pi and I would to know how can we simulate/mock the sensors (or GPIO) so I can test just my python code, mocking the Highs and Lows of the pins? 
Thanks in advance!
IF you just don't want to trust a software layer, you could try manually setting the pin high:
The GPIO pins on the Raspberry Pi work with a voltage of 3.3VDC.
Pins 1 & 17 on the P1-GPIO header outputs 3.3VDC.
You could CAREFULLY try to connect a jumper from Pin 1 or 17 to the GPIO input pin you want to test.  Connect it to test high, disconnect to test for low.
MAKE SURE YOU DON"T USE THE 5VDC GPIO PINS, YOU COULD/WILL DAMAGE/KILL YOUR PI!
Simulate Raspberry Pi GPIO signal