TST: completed refactoring of tests

unittests/test_cfood_metadata.py

unittests/test_converters.py

unittests/test_issues.py

unittests/test_json.py

unittests/test_macros.py

unittests/test_scalars_cfood.py

unittests/test_schema.py

unittests/test_table_converter.py

unittests/test_tool.py

unittests/test_tool_extended.py

unittests/test_variable_substitutions.py