update: ref -> reference (#1835)

* update: ref -> reference

sed -i \
  's/--ref[^e]/--reference/g' \
  $(grep -lr '\--ref[^e]')

doc/dev/TESTING.md

@@ -43,7 +43,7 @@ When contributing to F3D, it is necessary that new code is covered by a test in
 ### Application layer
 
 All application tests are initiated via the `CTest` (https://cmake.org/cmake/help/book/mastering-cmake/chapter/Testing%20With%20CMake%20and%20CTest.html) testing framework.
-`CTest` runs `f3d` with the `--output` and `--ref` arguments which renders an output image and compares it to a reference image. F3D compares the differences between the 2 images and compute a difference value and compare it to a threshold to check if a test passes or not.
+`CTest` runs `f3d` with the `--output` and `--reference arguments which renders an output image and compares it to a reference image. F3D compares the differences between the 2 images and compute a difference value and compare it to a threshold to check if a test passes or not.
 
 All aspects of the application test framework are handled in `application/testing/CMakeLists.txt`.