Increase test coverage

[kurosakishigure]

Test Description

Increase the scope of unit tests. Missing test cases can be found on Coveralls.

Rationale

Test coverage is low.

Additional Information

We can refer to the code marked as lacking tests on Coveralls and add corresponding test cases.

[kurosakishigure]

The file that has the greatest impact on coverage is handle.rs.

The key lines are:

https://github.com/kurosakishigure/katharsis/blob/215689fba57c1f6f1f2610e5a9e18bc2a90994e9/src/cmd/handle.rs#L46

When testing, we should think about how to simulate user input🤔.

Tips: We are considering adding a -y or --no-confirm parameter.