Restore visual diff to original behavior

This restores the following corner case:

When there is a difference, but it's only about
the case of the characters, don't want to show
the visual diff by default, but we offer the
feature to the user.

I also updated the tests the reflect the specs.
> Can use `[].some()` here.

Simplified in 9db20805e8270ae1eaf7c3eeb0deb6db5aedf703