I have developed an application using Kotlin and Swift languages, which has been installed and run on an iPhone. It can also be installed on an iPad. Do I need to go through a testing process to publish it on the app store? Also, as a developer from China, are there convenient payment channels for developers?
Do I need to go through a testing process
Yes, of course. And remind your app will not pass review if reviewer finds a bug.
But precise answer may depend on what you mean.
You need to test extensively: that means testing all the functions of your app in various conditions: for instance, if user has to enter a value, test with different values including "incorrect" values. Test also the performance if that is important for your app. If you write a user manual, that's a good way to be sure you test in a user perspective, not only a developer one.
But you are not required to go through a specific test method or process. It is up to you to select the best, possibly some tool to organise test.
You may have a look here: