diff --git a/lib/fs/fat/rules.mk b/lib/fs/fat/rules.mk
index b9f4dc3d..94dcc25c 100644
--- a/lib/fs/fat/rules.mk
+++ b/lib/fs/fat/rules.mk
@@ -7,6 +7,10 @@ MODULE_DEPS += lib/bio
 MODULE_DEPS += lib/fs
 MODULE_DEPS += lib/libcpp
 
+ifeq ($(call TOBOOL,WITH_TESTS),true)
+MODULE_DEPS += $(LOCAL_DIR)/test
+endif
+
 MODULE_SRCS += $(LOCAL_DIR)/dir.cpp
 MODULE_SRCS += $(LOCAL_DIR)/fat.cpp
 MODULE_SRCS += $(LOCAL_DIR)/file.cpp
diff --git a/lib/fs/fat/test/rules.mk b/lib/fs/fat/test/rules.mk
new file mode 100644
index 00000000..fcdc5920
--- /dev/null
+++ b/lib/fs/fat/test/rules.mk
@@ -0,0 +1,9 @@
+LOCAL_DIR := $(GET_LOCAL_DIR)
+
+MODULE := $(LOCAL_DIR)
+
+MODULE_DEPS += lib/fs/fat
+
+MODULE_SRCS += $(LOCAL_DIR)/test.cpp
+
+include make/module.mk
diff --git a/lib/fs/fat/test/test.cpp b/lib/fs/fat/test/test.cpp
new file mode 100644
index 00000000..e69de29b
diff --git a/lib/fs/spifs/rules.mk b/lib/fs/spifs/rules.mk
index b313d2b0..25c196c3 100644
--- a/lib/fs/spifs/rules.mk
+++ b/lib/fs/spifs/rules.mk
@@ -2,12 +2,14 @@ LOCAL_DIR := $(GET_LOCAL_DIR)
 
 MODULE := $(LOCAL_DIR)
 
-MODULE_SRCS += \
-	$(LOCAL_DIR)/spifs.c \
+MODULE_SRCS += $(LOCAL_DIR)/spifs.c
 
-MODULE_DEPS += \
-	lib/fs \
-	lib/cksum \
-	lib/bio
+ifeq ($(call TOBOOL,WITH_TESTS),true)
+MODULE_DEPS += $(LOCAL_DIR)/test
+endif
+
+MODULE_DEPS += lib/bio
+MODULE_DEPS += lib/cksum
+MODULE_DEPS += lib/fs
 
 include make/module.mk
diff --git a/project/stm32f746g-disco-test.mk b/project/stm32f746g-disco-test.mk
index adfeef00..ff9af16c 100644
--- a/project/stm32f746g-disco-test.mk
+++ b/project/stm32f746g-disco-test.mk
@@ -2,9 +2,7 @@ include project/target/stm32f746g-disco.mk
 include project/virtual/test.mk
 include project/virtual/minip.mk
 
-MODULES += \
-	lib/fs \
-    app/loader
+MODULES += app/loader
 
 include project/virtual/fs.mk
 
diff --git a/project/virtual/fs.mk b/project/virtual/fs.mk
index 76bc2ed7..d9de1026 100644
--- a/project/virtual/fs.mk
+++ b/project/virtual/fs.mk
@@ -1,10 +1,9 @@
-# modules related to a file system layer
+# modules related to a file system layer some file system implementations
 
 MODULES += \
     lib/fs \
     lib/fs/ext2 \
     lib/fs/fat \
     lib/fs/spifs \
-    lib/fs/spifs/test \
     lib/fs/memfs
 
diff --git a/project/virtual/test.mk b/project/virtual/test.mk
index 78ec94c1..1dc71681 100644
--- a/project/virtual/test.mk
+++ b/project/virtual/test.mk
@@ -11,3 +11,9 @@ MODULES += \
   lib/debugcommands \
   lib/unittest \
   lib/version
+
+# set a build system variable for other modules to include test code
+# on their own.
+WITH_TESTS := true
+GLOBAL_DEFINES += WITH_TESTS=1
+