Upgraded all test to use declare instead of echo

[UrsaDK]

This simplifies comparing bash builtin getopts and getopts_long, especially where one sets a blank variable, while the other one unsets it instead.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (936fdd5) to head (e12f575).
Report is 1 commits behind head on master.

Additional details and impacted files