Fix/operators support 3 variants

[tilucasoli]

Issue ticket number

closes #154

Describe your changes

• More the test case to operators feature;
• Rename some variable's name;
• Change the way the function matches identify a variant matching;

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• Test (adding missing tests, refactoring tests; no production code change)

Checklist before requesting a review

• I have performed a self-review of my code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works