Fixed load control object and unit test. Added recipe to Makefile for Zephyr OS twister unit testing. (#710)

Makefile

@@ -450,3 +450,16 @@ test:
 .PHONY: retest
 retest:
 	$(MAKE) -s -j -C test retest
+
+# Zephyr unit testing with twister
+# expects zephyr to be installed in ../zephyr in Workspace
+# expects ZEPHYR_BASE to be set. E.g. source ../zephyr/zephyr-env.sh
+# see https://docs.zephyrproject.org/latest/getting_started/index.html
+TWISTER_RESULTS=../twister-out.unit_testing
+.PHONY: twister
+twister:
+	$(ZEPHYR_BASE)/scripts/twister -O $(TWISTER_RESULTS) -p unit_testing -T zephyr/tests
+
+.PHONY: twister-clean
+twister-clean:
+	-rm -rf $(TWISTER_RESULTS)