Add unit test framework and simple unit test example

.vscode/settings.json

@@ -2,6 +2,7 @@
     "files.associations": {
         "stdbool.h": "c",
         "cstdlib": "c",
-        "ftdi_dev.h": "c"
+        "ftdi_dev.h": "c",
+        "time.h": "c"
     }
 }

Makefile

@@ -14,12 +14,16 @@ UNIT_TEST_OBJ_DIR = $(OBJ_DIR)/$(UNIT_TEST_SRC_DIR)
 
 INCLUDES := inc
 
+#Alpine Linux names libftdi libftdi1
+ifneq "$(findstring Alpine,$(shell head -1 /etc/issue))" ""
+INCLUDES += /usr/include/libftdi1
+endif
+
 ifneq "$(findstring $(MAKECMDGOALS), build_unit_test exec_unit_test)" ""
 INCLUDES += test/inc
 else
 #Alpine Linux names libftdi libftdi1
 ifneq "$(findstring Alpine,$(shell head -1 /etc/issue))" ""
-INCLUDES += /usr/include/libftdi1
 LIBS := ftdi1
 else
 LIBS := ftdi

test/unit/test_gpio.c

@@ -1,6 +1,7 @@
 #include <assert.h>
 #include <stdlib.h>
 #include <stdbool.h>
+#include <time.h>
 
 #include <fff.h>
 #include <utest.h>