Hi,
You can use the evtest application for testing the senor.
Maybe it's necessary to enable the sensor, for example enabling FXOS8700 on the i.MX7D SabreSD board:
$ echo 1 > /sys/devices/virtual/misc/FreescaleAccelerometer/enable
$ echo 1 > /sys/devices/virtual/misc/FreescaleMagnetometer/enable
Best regards,
Breno Lima