add compare log test

tests/README.md

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+# Testing examples
+
+Examples are tested using tool [htrun](https://github.com/ARMmbed/mbed-os-tools/tree/master/packages/mbed-host-tests) and templated print log. 
+
+To run the test, use following command after you build the example:
+```bash
+$ mbedhtrun -d <MOUNT_POINT> -p <SERIAL_PORT> -m <TARGET> -f ./BUILD/<TARGET>/<TOOLCHAIN>/<BUILT_IMAGE> --compare-log tests/<LOG_FILE>
+```
+For example:
+```bash
+$ mbedhtrun -d /media/user01/DAPLINK -p /dev/ttyACM0 -m DISCO_L475VG_IOT01A -f ./BUILD/DISCO_L475VG_IOT01A/GCC_ARM/mbed-os-example-ble.bin --compare-log tests/broadcast.log
+```
+
+
+More details about `htrun` are [here](https://github.com/ARMmbed/mbed-os-tools/tree/master/packages/mbed-host-tests#testing-mbed-os-examples).
+

tests/broadcast.log

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+DEVICE MAC ADDRESS: ([0-9a-fA-F]{2}:){5}[0-9a-fA-F]{2}