[lib][fs] move the existing test code into its own sub module lib/fs/test

No real functional change, just following the pattern of moving unittest
code into a sub module that is picked up by the build system when
WITH_TESTS is set.

lib/fs/rules.mk

@@ -5,6 +5,9 @@ MODULE := $(LOCAL_DIR)
 MODULE_SRCS += $(LOCAL_DIR)/debug.c
 MODULE_SRCS += $(LOCAL_DIR)/fs.c
 MODULE_SRCS += $(LOCAL_DIR)/shell.c
-MODULE_SRCS += $(LOCAL_DIR)/test.c
+
+ifeq ($(call TOBOOL,WITH_TESTS),true)
+MODULE_DEPS += $(LOCAL_DIR)/test
+endif
 
 include make/module.mk

lib/fs/test/rules.mk

@@ -0,0 +1,10 @@
+LOCAL_DIR := $(GET_LOCAL_DIR)
+
+MODULE := $(LOCAL_DIR)
+
+MODULE_DEPS += lib/fs
+MODULE_DEPS += lib/unittest
+
+MODULE_SRCS += $(LOCAL_DIR)/test.c
+
+include make/module.mk

lib/fs/test/test.c

@@ -11,8 +11,6 @@
 #include <string.h>
 #include <string.h>
 #include <stdio.h>
-
-#if WITH_LIB_UNITTEST
 #include <lib/unittest.h>
 
 // returns true if the input path passed through the path normalization
@@ -109,5 +107,3 @@ BEGIN_TEST_CASE(fs_tests);
 RUN_TEST(test_path_normalize);
 RUN_TEST(test_stdio_fs);
 END_TEST_CASE(fs_tests);
-
-#endif // WITH_LIB_UNITTEST