Added tests

Author: IhorShevchuk

libpiper/CMakeLists.txt

@@ -148,15 +148,7 @@ target_link_libraries(piper
 )
 
 # ---- piper exe ---
-
-add_executable(piper_exe src/main.cpp
-                         src/wavfile.cpp
-                         include/wavfile.hpp
-              )
-target_link_libraries(piper_exe
-                      piper
-)
-
+add_subdirectory(src/main)
 # ---- install ---
 
 include(GNUInstallDirs)