fixed test invocation via ctest

With current syntax `add_test(testname Exename)` binary can't be found because it placed in CMAKE_BINARY_DIR\[Debug|Release]

With new syntax `add_test(NAME <name> COMMAND <command> [arg1 [arg2 ...]])` 
COMMAND specifies an executable target (created by add_executable) will automatically be replaced by the location of the executable created at build time.

Ref: http://cmake.org/cmake/help/v2.8.12/cmake.html#command:add_test