Fix negative basket total due to shipping tax residue

[torreytsui]

Description

A negative basket total is produced when:

• tax was applied;
• shipping was calculated and saved; and
• basket is emptied

This PR fixes the issue by completing an earlier return on tax total collector that failed to unset taxed shipping total information.

Fixed Issues (if relevant)

No directly related issue found

Manual testing scenarios

1. Set up tax to 20%

2. Set up tax settings like below

   

3. Sign in on front-end

4. Add a default shipping address that will result in 20% tax rate

5. Add a product to basket

6. Go to checkout page

7. Select default shipping address and select shipping method

8. Step to billing (At this point, shipping tax should be calculated and show up on the breakdown)

9. Go to basket page

10. Empty the basket by removing the only product from it

Expected result

Basket total should become 0

Actual result

Basket total become negative (e.g., -1)

/customer/section/load/?sections=cart

DEMO

http://recordit.co/vERAS5KL1x

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[dmanners]

Hi @torreytsui thank you for this pull request. I can see that an integration test to cover this case, or one to make sure that the negative case does not happen any more would be very beneficial here.

Would you be able to have a look into this for me?

[torreytsui]

HI @dmanners, thanks for the reply. I'm still unable to replicate the issue on vanilla 2.2. It may be caused by some customisation. I will close this PR now.

[torreytsui]

Hi @dmanners, I managed to replicate the issue on a vanilla 2.2 env. Updated the steps and could you please have a look and see if you can replicate it on your side?

[dmanners]

Thanks @torreytsui I will see what I can do and update you on the progress.

[magento-engcom-team]

@torreytsui thank you for contributing. Please accept Community Contributors team invitation here to gain extended permissions for this repository.

[magento-engcom-team]

Hi @torreytsui. Thank you for your contribution.
Changes from your Pull Request will be available with the upcoming 2.2.5 release.