Coverage report for CMake

[david-drinn]

The coverage report seemed to have been implemented with #1139 and #1394, but at some point I guess support was removed. There's no longer any mention of --coverage in the CMake files, and if I provide the -DCOVERAGE=ON as in the scripts/travis_ci_build.sh file, CMake warns that it's not used. I can't find any relevant make targets for coverage as mentioned in the docs.

@offa mentions in #1394 (comment) that gcovr is easy to use, so I'm trying to work it out now. But it would be nice if it was added back to the CMake builds.

[thetic]

The COVERAGE option was intended to enable coverage for CppUTest's own tests.
Enable coverage by setting the appropriate compile options in your own project.
For example, for GCC:

add_compile_options(--coverage)

(See https://cmake.org/cmake/help/latest/command/add_compile_options.html.)

You can also add flags ad hoc from the command line when configuring your project:

cmake -DCMAKE_C_FLAGS=--coverage -DCMAKE_CXX_FLAGS=--coverage # ...

(See https://cmake.org/cmake/help/latest/variable/CMAKE_LANG_FLAGS.html.)

gcovr is great for generating reports once you've run your instrumented tests.
You should be able to simply run gcovr --txt or gcovr --html from the working directory.