automate testing of large files

[zooko]

Per #346 (increase share-size field to 8 bytes, remove 12GiB filesize limit), it appears that we've deployed some bugs in Tahoe v1.0 which only manifest when you try to upload a file larger than about 4 billion bytes.

This reminds us that we really want to have automated testing for these parts of the code. This ticket is to make a test which is automated in the sense that a human isn't required to do anything in order to perform the test and collect the results. There will be a separate ticket for the separate question of whether tests of large files should be automatically launched by e.g. a buildbot policy without human intervention.

[zooko]

See also #437 (automatically schedule tests of large files).

[zooko]

Moving this out of the 1.3.1 Milestone.

[zooko]

This was long ago fixed by 6c4019ec33e7a253 (see also 466014f66fbccff7, 8c37b8e3af2f4d1b).

(But see also #437 (automatically scheduled tests of large files).)

[davidsarah]

Replying to zooko:

This was long ago fixed by 6c4019ec33e7a253 (see also 466014f66fbccff7, 8c37b8e3af2f4d1b).

Well, test_large_share is currently disabled. But yes, the test exists, and it passed last time I tested it on my machine (Windows), during the 1.8.0 release process.

Perhaps the test could detect platforms that are known to support sparse files, so that we can reenable it on those platforms? That would be a reasonable alternative to #437, I think.