Split up basic interface test file for readability

Author: egpbos

test/CMakeLists.txt

@@ -95,7 +95,9 @@ include_directories(${XTENSOR_FFTW_INCLUDE_DIR})
 include_directories(${GTEST_INCLUDE_DIRS})
 
 set(XTENSOR_FFTW_TESTS
-        basic_interface.cpp
+        basic_interface_fft.cpp
+        basic_interface_rfft.cpp
+        basic_interface_hfft.cpp
         helper.cpp
         examples.cpp
 )