test(validator): add tests for checking a validation on checkbox inputs

[Icyscools]

On PR #205, I did solve a problem on #141 which fix a validation on checkbox inputs, but I didn't add a test for it.

To ensure that our code is still functioning properly, we should add some tests to it. However, I'm unsure how to create a test case for this issue, so I need some help. 😅

In this issue, we need to

• add some tests on a validator package for testing fix(validator): use a checked attribute for required validation in checkboxes #205