Add unit test framework and simple unit test example

Makefile

@@ -1,6 +1,6 @@
 CROSS_COMPILE ?=
 
-TARGET_FILE ?= test
+TARGET_FILE ?= ftdi_gpio
 
 CC = $(CROSS_COMPILE)gcc
 CPP = $(CROSS_COMPILE)cpp
@@ -9,9 +9,14 @@ CHECK = cppcheck
 SRC_DIR = src
 OBJ_DIR = obj
 BIN_DIR = bin
+UNIT_TEST_SRC_DIR = test/unit
+UNIT_TEST_OBJ_DIR = $(OBJ_DIR)/$(UNIT_TEST_SRC_DIR)
 
 INCLUDES := inc
 
+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
@@ -19,6 +24,7 @@ LIBS := ftdi1
 else
 LIBS := ftdi
 endif
+endif
 
 LD_FLAGS :=
 C_FLAGS := -O0 -g -Wall -Wextra -Werror
@@ -28,18 +34,34 @@ CHECK_CLAGS := --enable=all --template=gcc --error-exitcode=1 --suppress=missing
 C_SRCS = $(wildcard $(SRC_DIR)/*.c)
 C_OBJS = $(patsubst $(SRC_DIR)%,$(OBJ_DIR)%,$(patsubst %.c,%.o,$(C_SRCS)))
 
+UNIT_TEST_SRCS = $(wildcard $(UNIT_TEST_SRC_DIR)/*.c) $(filter-out %main.c,$(C_SRCS))
+UNIT_TEST_OBJS = $(patsubst $(SRC_DIR)%,$(OBJ_DIR)%,$(patsubst $(UNIT_TEST_SRC_DIR)%,$(UNIT_TEST_OBJ_DIR)%,$(patsubst %.c,%.o,$(UNIT_TEST_SRCS))))
+
 OBJS = $(C_OBJS)
 
 TARGET = $(BIN_DIR)/$(TARGET_FILE)
+UNIT_TEST_TARGET = $(BIN_DIR)/$(UNIT_TEST_SRC_DIR)/$(TARGET_FILE)
+
 THIS_MAKEFILE := $(lastword $(MAKEFILE_LIST))
 
 .PHONY: all
 all: $(TARGET)
 
+.PHONY: unit_test
+build_unit_test: $(UNIT_TEST_TARGET)
+
+.PHONY: unit_test
+exec_unit_test: $(UNIT_TEST_TARGET)
+	$(UNIT_TEST_TARGET)
+
 .PHONY: check
 check: $(C_SRCS)
 	$(CHECK) $(CPP_FLAGS) $(CHECK_CLAGS) $(C_SRCS)
 
+$(UNIT_TEST_TARGET): $(UNIT_TEST_OBJS) $(THIS_MAKEFILE)
+	@mkdir -p $(BIN_DIR)/$(UNIT_TEST_SRC_DIR)
+	$(CC) $(C_FLAGS) $(LD_FLAGS) $(UNIT_TEST_OBJS) $(addprefix -l,$(LIBS)) -o $@
+
 $(TARGET): $(OBJS) $(THIS_MAKEFILE)
 	@mkdir -p $(BIN_DIR)
 	$(CC) $(C_FLAGS) $(LD_FLAGS) $(OBJS) $(addprefix -l,$(LIBS)) -o $@
@@ -49,13 +71,23 @@ $(OBJ_DIR)/%.d: $(SRC_DIR)/%.c
 	@mkdir -p $(OBJ_DIR)
 	$(CPP) -MM -MF $@ -MP -MT $(patsubst %.d,%.o,$@) $(CPP_FLAGS) $(patsubst $(OBJ_DIR)/%.d,$(SRC_DIR)/%.c,$@)
 
+.PRECIOUS: $(UNIT_TEST_OBJ_DIR)/%.d
+$(UNIT_TEST_OBJ_DIR)/%.d: $(UNIT_TEST_SRC_DIR)/%.c
+	@mkdir -p $(UNIT_TEST_OBJ_DIR)
+	$(CPP) -MM -MF $@ -MP -MT $(patsubst %.d,%.o,$@) $(CPP_FLAGS) $(patsubst $(UNIT_TEST_OBJ_DIR)/%.d,$(UNIT_TEST_SRC_DIR)/%.c,$@)
+
 $(OBJ_DIR)/%.o: $(SRC_DIR)/%.c $(OBJ_DIR)/%.d
 	@mkdir -p $(OBJ_DIR)
 	$(CC) -c $(CPP_FLAGS) $(C_FLAGS) $< -o $@
 
+$(UNIT_TEST_OBJ_DIR)/%.o: $(UNIT_TEST_SRC_DIR)/%.c $(UNIT_TEST_OBJ_DIR)/%.d
+	@mkdir -p $(UNIT_TEST_OBJ_DIR)
+	$(CC) -c $(CPP_FLAGS) $(C_FLAGS) $< -o $@
+
 .PHONY: clean
 clean:
 	rm -rf $(OBJS) $(patsubst %.o,%.d,$(OBJS)) $(TARGET)
+	rm -rf $(UNIT_TEST_OBJS) $(patsubst %.o,%.d,$(UNIT_TEST_OBJS)) $(UNIT_TEST_TARGET)
 
 ifneq ($(MAKECMDGOALS),clean)
 -include $(patsubst %.o,%.d,$(OBJS))