zint/frontend/tests

Zint frontend test suite
------------------------

See <project-dir>/backend/tests/README to see how to build the test suite.
In addition to the setup for the backend tests, the environment needs to be
able to find the `zint` application using that name. In UNIX-like systems
this can be configured by prepending the PATH variable with the frontend's
directory inside the build directory:

cd <build-dir>
export PATH=$(pwd)/frontend:${PATH}


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the frontend test will be automatically run by cmake's ctest, however manual
invocation is also possible:

cd <build-dir>/frontend/test
./test_args

As with the backend tests, individual test functions and single dataset items
can be run using '-f <func-name>' and '-i <index>' etc.