tests/test-diff-issue2761.t

parsers: clarify documentation of test-parseindex2.py

This change updates and improves the description of test-parseindex2.py.
In particular, it removes language that can be interpreted to mean that the
test module checks only the C implementation of parsers.parse_index2().
Rather, the module checks parsers.parse_index2(), which can be either the
C or pure Python implementation, depending on which version is being used.

As of e57c532c3835, the module also does more than just compare the return
value with the original Python implementation.

Test issue2761

  $ hg init

  $ touch to-be-deleted
  $ hg add
  adding to-be-deleted
  $ hg ci -m first
  $ echo a > to-be-deleted
  $ hg ci -m second
  $ rm to-be-deleted
  $ hg diff -r 0

Same issue, different code path

  $ hg up -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ touch does-not-exist-in-1
  $ hg add
  adding does-not-exist-in-1
  $ hg ci -m third
  $ rm does-not-exist-in-1
  $ hg diff -r 1