Use test-unit gem instead of test-framework of ruby repo

[hsbt]

I replaced test-framework provided by ruby/ruby repo to test-unit gem and the additional assertions named CoreAssertions.

This change makes unifying to assertion verb with test-unit gem.

[kou]

Thanks.
I'll add some methods to test-unit gem to reduce more files.

[hsbt]

@kou What can I do the next step? If you are okay to this, I will merge this.

I'll add some methods to test-unit gem to reduce more files.

It's great for me.

[kou]

Could you wait for a few days? I want to review all changes and try this on local. For example, I think that we should not remove is_output_field_separator_deprecated check in test/lib/with_different_ofs.rb. (I think that we need to check it with $VERBOSE = true.)

[hsbt]

Could you wait for a few days?

It's ok, no problem.

I think that we should not remove is_output_field_separator_deprecated check in test/lib/with_different_ofs.rb

👍 I picked this helper from ruby/ruby repo originally. It's better to adjust to CSV library.

[kou]

• Fixed WithDifferentOFS.
• Removed CoreAssertions entirely by adding needed assertions to test-unit.

[hsbt]

Thanks!