Set default tax_rate to destination

[kt-12]

Changes proposed in this Pull Request:

The Tax Rate (the UI will be removed later; see #2490), shown on the second screen when a US country is selected, must default to destination.

Closes #2491.

Set the default value in the scheme property to destination. After the change, /wp-json/wc/gla/mc/settings does show default tax_rate as destination, in comparison to early `null. This was also reflected in Tax Rate UI.
See the before and after change screenshot of the setting endpoint.

Screenshots:

Before: you can see tax_rate is null

After: you can see tax_rate is destination

Detailed test instructions:

1. Move to onboarding second screen.
2. While on the second page, clear the option npm run wp-env run cli wp option delete gla_merchant_center to ensure it was not previously saved on a previous test.
3. Reload the 2nd screen, and under location select North American. You should see UI for Tax rate (required for U.S. only) below.
4. Check if the default option is My store uses destination-based tax rates..
5. Check db. npm run wp-env run cli wp option get gla_merchant_center. Note to QA:- You need to check this again once the UI removal is complete (Onboarding: Remove Tax Rates Selection UI #2490)

Additional details:

Changelog entry

Tweak - Set the default value of the tax rate to destination-based during onboarding.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 65.6%. Comparing base (5af0314) to head (d6f5658).
Report is 42 commits behind head on feature/2458-streamline-onboarding.

Additional details and impacted files

@@                           Coverage Diff                           @@
##             feature/2458-streamline-onboarding   #2543      +/-   ##
=======================================================================
+ Coverage                                  63.8%   65.6%    +1.8%     
- Complexity                                    0    4580    +4580     
=======================================================================
  Files                                       326     475     +149     
  Lines                                      5086   17891   +12805     
  Branches                                   1229       0    -1229     
=======================================================================
+ Hits                                       3247   11737    +8490     
- Misses                                     1672    6154    +4482     
+ Partials                                    167       0     -167     

Flag	Coverage Δ
js-unit-tests	?
php-unit-tests	65.6% <100.0%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
.../Controllers/MerchantCenter/SettingsController.php	98.5% <100.0%> (ø)

... and 800 files with indirect coverage changes

[joemcgill]

This looks like it will work. Thanks for adding a new test class for the MerchantCenter\SettingsController.

[ankitguptaindia]

QA/Test Report- ✅

Testing Environment -

• WordPress: 6.6.1
• Theme: Storefront Version: 4.6.0 / Twenty Twenty-Four Version: 1.2
• WooCommerce - Version 9.1.4
• PHP: 8.3
• Web Server: Nginx
• Browser: Chrome - Version 127
• OS: macOS Sonoma 14.6

Steps to Test- Please follow the steps mentioned in the PR description. If you are using Local software for your testing environment instead of 'wp-env' / Docker-based environment. Use this command to delete the option from DB - wp option delete gla_merchant_center

Test Results -

All related tests are working as expected with this PR.

• When intentionally saving the other option, i.e., 'My store does not use destination-based tax rates', and deleting the option setting from the database, after a page refresh, it shifts back to the default option as set by this PR. ✅

• When the merchant uses the second option, i.e., 'My store does not use destination-based tax rates', and moves to the next screen and then back to the previous screen, it keeps the desired option selected. ✅

• On the fresh onboarding screen, it keeps 'My store uses destination-based tax rates.' selected by default. ✅

• When the Audience and Store Address are not US-based, this option should not be displayed. ✅

• When the Store has a non-US-based address and the merchant selects/adds the US in the audience option from the 'Configure product listings' screen, it shows the 'My store uses destination-based tax rates.' option selected by default. ✅

Functional Demo / Screencast -

Recording.798.mp4

Plugin file with this PR-specific build google-listings-and-ads.zip

[mikkamp]

Thanks for the changes.

I tested fetching the settings and received the expected default:

{
    "shipping_rate": null,
    "shipping_time": null,
    "tax_rate": "destination",
    "website_live": false,
    "checkout_process_secure": false,
    "payment_methods_visible": false,
    "refund_tos_visible": false,
    "contact_info_visible": false
}

I also tested setting some basic values without taxes and still got the expected default set:

{
    "status": "success",
    "message": "Merchant Center Settings successfully updated.",
    "data": {
        "shipping_rate": "automatic",
        "shipping_time": "flat",
        "tax_rate": "destination",
        "website_live": true,
        "checkout_process_secure": true,
        "payment_methods_visible": true,
        "refund_tos_visible": true,
        "contact_info_visible": true
    }
}

The code all looks good to me. Thanks for adding the extra unit test, it runs well.

There is no harm in merging this PR to develop, but that means it will get included in a release next Tuesday. Since it's going to be combined with #2542 I'd suggest to target a feature branch where both these PR's can get merged to.