Add example for the weak linking

examples/weak_linking/Makefile

@@ -0,0 +1,48 @@
+
+BUILD_DIR = ../../build
+INCLUDE_DIRS = -I "../../" -I "./src/"
+
+BUILD_DIR_FAKE =  $(BUILD_DIR)/weak_linking
+CC = gcc
+WEAK_FLAGS=-Wall -DFFF_FUNCTION_ATTRIBUTES="__attribute__((weak))"
+
+$(BUILD_DIR_FAKE)/%.o: test/%.c
+	@echo "Compiling "$@
+	$(CC) $(WEAK_FLAGS) $(INCLUDE_DIRS) -g -O0 -c $< -o $@ 
+	
+
+
+
+FAKE_OBJECTS = $(BUILD_DIR_FAKE)/display.fake.o $(BUILD_DIR_FAKE)/sensor.fake.o $(BUILD_DIR_FAKE)/sensor.fake.o $(BUILD_DIR_FAKE)/error.fake.o  $(BUILD_DIR_FAKE)/bus.fake.o $(BUILD_DIR_FAKE)/test_common.o
+
+TEST_BINARIES = $(BUILD_DIR_FAKE)/test_main $(BUILD_DIR_FAKE)/test_display $(BUILD_DIR_FAKE)/test_sensor 
+mkdir:
+	mkdir -p $(BUILD_DIR_FAKE)/
+
+clean:
+	rm -rf $(BUILD_DIR_FAKE)/ 
+
+$(BUILD_DIR_FAKE)/libfakes.a:  $(FAKE_OBJECTS)
+	ar r $@  $^
+
+#
+# First case where we need __weak__ linking: if we have the build objects (for some reason) in order where the fake
+# object compes first 
+$(BUILD_DIR_FAKE)/test_display: ./test/display.test.c $(BUILD_DIR_FAKE)/libfakes.a ./src/display.c
+	$(CC) $(WEAK_FLAGS) $(INCLUDE_DIRS) -o $@ $^
+
+#
+# Second case where we need weak linking: If we use a object from the fake object -> gcc linker will include it
+# One can go around also in another way: by making the fake objects in separate files. 
+#
+$(BUILD_DIR_FAKE)/test_sensor: ./test/sensor.test.c ./src/sensor.c $(BUILD_DIR_FAKE)/libfakes.a
+	$(CC) $(WEAK_FLAGS) $(INCLUDE_DIRS) -o $@ $^
+
+#
+# Third case: we want to mock one function but not all.
+#
+$(BUILD_DIR_FAKE)/test_main: ./test/main.test.c ./src/main.c $(BUILD_DIR_FAKE)/libfakes.a
+	$(CC) $(WEAK_FLAGS) $(INCLUDE_DIRS) -o $@ $^
+
+
+all: mkdir $(TEST_BINARIES)