Error when using a NDK built Library which depend on another one in a Unity project

I want to create a native C++ program and use it on Android and I learned to do so using the Android NDK. I've even created a test plugin (lib*.so ) which worked perfectly. But when I created a plugin which depend on the first one (meaning another shared library created with the NDK) and used it in a Unity project, it didn't work. I've got this error :

 E/Unity   ( 4719): Unable to find MyLib
 I/Unity   ( 4719): DllNotFoundException: MyLib
 I/Unity   ( 4719):   at (wrapper managed-to-native) TestDLLScript:Foo ()
 I/Unity   ( 4719):   at TestDLLScript.Start () [0x00000] in <filename unknown>:0
 I/Unity   ( 4719):
 I/Unity   ( 4719): (Filename:  Line: -1)
 I/Unity   ( 4719):

Is this a problem from Unity or is there some procedure that I need to follow to make this work?

Also here is my plugin make file, even though I don't think that the problem came from it (since it built without any error or warning) :

 LOCAL_PATH := $(call my-dir)
 
 include $(CLEAR_VARS)
 LOCAL_MODULE := TestDLL
 LOCAL_SRC_FILES := libs/$(TARGET_ARCH_ABI)/libTestDLL.so
 LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)/source
 include $(PREBUILT_SHARED_LIBRARY)
 
 include $(CLEAR_VARS)
 LOCAL_MODULE := MyLib
 LOCAL_SRC_FILES += MyLibrary.cpp
 LOCAL_SHARED_LIBRARIES += TestDLL
 include $(BUILD_SHARED_LIBRARY)