[In-app Purchases] Add unit tests for InAppPurchaseStore

[koke]

Closes: #8057

Description

This adds some unit tests for the InAppPurchaseStore. I haven't tested every single aspect since it seems like MockNetwork can only simulate responses and not validate that an endpoint was called. So I'm not sure how to test the transaction listener, but I feel like this tests already touch the most critical points and it's an improvement over no tests 🤷🏽

Note that I had to bring back the local StoreKit configuration file for this to work. After testing different variations, I realized that there's no need to set the Xcode scheme to use it. As long as the file is included in the test bundle, when you initialize the SKTestSession, it will switch to the local configuration. The only tricky aspect was that I had to add the tests in the WooCommerce project, since Yosemite tests run without a host application and it doesn't seem like StoreKitTest works that way.

Testing instructions

Unit tests should pass

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• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-woocommerce]

	Warnings
⚠️	This PR is assigned to a milestone which is closing in less than 2 days Please, make sure to get it merged by then or assign it to a later expiring milestone

Generated by 🚫 dangerJS

[koke]

I'm having second thoughts about this. I added the StoreKit configuration with sync enabled, but if we're only going to use this for testing, maybe I should convert to local and ensure it only has the debug product? I'm not sure we want the whole product catalog synced to a public repo.

[toupper]

Yeah, if it's only for unit testing I would convert it to local and only add the debug product, no need to have the whole product catalog even if I don't see huge security issues with that.

[wpmobilebot]

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[toupper]

Yeah, if it's only for unit testing I would convert it to local and only add the debug product, no need to have the whole product catalog even if I don't see huge security issues with that.

[toupper]

Great job! ILGTM, now we have vital parts tested 👍

I haven't tested every single aspect since it seems like MockNetwork can only simulate responses and not validate that an endpoint was called.

That's a good point. It seems to me like MockNetwork is easy to extend to validate that an endpoint was called; do you think it is worth doing that (In other PR/issue)? I see value in that, not only for this task, but for other cases when we want to test that an endpoint was called.

[koke]

👍🏽 I'll take a look at extending MockNetwork in a separate PR