Expand tests coverage

[martynmjones]

Describe the issue

As part of the recent efforts to improve consistency across event data structures, #245 to avoid introducing issues in the future.

Now that there is a framework in place for unit testing the backend we should look to expand test coverage for the extension.

E2E tests

In #385 we added coverage for E2E tests, as a follow up to that PR we have the following list of things which aren't being tested:

• Remove from cart with shortcode [woocommerce_cart] isn't always tracked because of immediate page redirect (not in E2E)
• Remove from cart / Begin checkout is not consistent between blocks and shortcode, category and variation data differ.
• Change cart quantity is not tracked with shortcode [woocommerce_cart] or with blocks (PR Remove unused function from formatters #375 removes it)
• Add shipping info doesn't seem to be used anywhere (mentioned in Remove unused function from formatters #375 (comment))
• Select content is difficult to test if it is followed up by a page redirect (no E2E tests written yet)
• begin_checkout logs total item price (including discounts and price * quantity), purchase logs product object price (not final price we paid in the order). Should these be consistent?
• When we hook into woocommerce_add_to_cart, should we get final price from cart_item_data? Otherwise we'll track product prices vs. discounted price.
• When we change the settings to redirect to cart page after add_to_cart, do we still capture all details?
• Testing with grouped / bundled products (grouped product seems to only track first product added to cart)
• Shipping total and Tax total in purchase event
• Tests for the All Products block (no longer used for the default shop page)