Ensure that tests do not interact with the users remote data manager and cache

[Cadair]

Following on from #3124 and #3550 we should really come up with a nice way to ensure that when tests are run locally we are not interacting with the users local cache.

[sashank27]

I believe this issue still persists. Any insights on how to proceed?

[vn-ki]

@sashank27 If you look at the changes made in #3550 you can see that there was already some code to do just this. But this was removed because it would have test related code in the actual codebase itself. This is not ideal.

So the essense of this issue is to figure out a good way to make the data manager tests not actually touch the local cache in some way. You could use the code removed in #3550 as a starting point as well as this fixture.

sunpy/sunpy/conftest.py

Lines 62 to 90 in 2eb3494

	@pytest.fixture()
	def sunpy_cache(mocker, tmp_path):
	"""
	Provide a way to add local files to the cache. This can be useful when mocking
	remote requests.
	"""
	from types import MethodType
	from sunpy.data.data_manager.cache import Cache
	from sunpy.data.data_manager.storage import InMemStorage
	from sunpy.data.data_manager.downloader import ParfiveDownloader
	cache = Cache(
	ParfiveDownloader(),
	InMemStorage(),
	tmp_path,
	None
	)
	def add(self, url, path):
	self._storage.store({
	'url': url,
	'file_path': path,
	'file_hash': 'none', # hash doesn't matter
	})
	cache.add = MethodType(add, cache)
	def func(mocked):
	mocker.patch(mocked, cache)
	return cache
	yield func

But I have to warn you this might be time consuming to pursue as it is more thinking and less coding.

In hindsight this might be a effort high issue.