Test Back-Pressure

[bvand]

There are currently no tests confirming that back-pressure is working correctly. We should add such a test so that future changes don't break back-pressure.

The test could "create a dummy API server endpoint that takes a long time to reply and see if the source gets paused when the high water mark is reached" (see #702).

[alanshaw]

@bvand are you working on adding these (as you mentioned in #702)?

[bvand]

@alanshaw I haven't done any work on this, feel free to pick it up!

[achingbrain]

Everything is async iterators now, which have a back pressure mechanism built in. Please open a new issue against ipfs/js-ipfs if this is still required.