gitignore was keeping it off the repository, and we hadn't noticed.
The file weighs 1.6MB, but it's a great way to test with a real index
with the right size and signature. Moreover, we likely won't be updating
this file often - perhaps once every couple of years, as the index
format progresses.
Most importantly, the file is not part of any importable Go package, so
it should never find its way to a vendor folder or a module archive.
The F-Droid index format contains absolute download urls, so setting up
a custom config for the tests with the original index file won't work
when dowlnoading APKs. Those will still get downloaded from f-droid.org.
To fix that, use http.Client.Transport instead of a custom config. This
requires less code, introduces less test code in non-test files, and
means we can use the default config in the tests.
Daniel Martí