I am confused as android guide says two different things about the same thing.
It says the benefit of using developer account is that you don't have to upload an APK for static response testing.
On another note, it says, the static response testing only applies to app uploaded (not necesserly published).
SOOO Whats the correct answer: If I don't upload the apk and I use my developer account, I get the Not_Market_manager response. Does that mean I have to always upload my apk for testing?
Yes. Upload, but don't publish, the APK.
Previously, you could publish a "draft" version of your app for testing. This functionality is no longer supported. Instead, there are two ways you can test how a pre-release app functions on the Google Play store:
You can publish an app to the alpha or beta distribution channels. This makes the app available on the Google Play store, but only to the testers you put on a "whitelist".
In a few cases, you can test Google Play functionality with an unpublished app. For example, you can test an unpublished app's in-app billing support by using static responses, special reserved product IDs that always return a specific result (like "purchased" or "refunded").
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