UTILS:
  $ reset() {
  >   cd ..
  >   rm -rf a
  >   hg init a
  >   cd a
  > }

TEST: incomplete requirements handling (required extension excluded)
  $ hg init a
  $ cd a
  $ cat >> .hg/hgrc <<EOF
  > [extensions]
  > drop=
  > EOF

  $ hg drop 1
  extension rebase not found
  abort: required extensions not detected
  [255]

SETUP: Properly setup all required extensions
  $ cat >> .hg/hgrc <<EOF
  > [extensions]
  > rebase=
  > drop=
  > [experimental]
  > evolution=all
  > EOF

TEST: handling no revision provided to drop
  $ hg drop
  abort: no revision to drop was provided
  [255]

TEST: aborting when drop called on root changeset
  $ hg debugbuilddag +1
  $ hg log -G -T '{rev} {desc|firstline}'
  o  0 r0
  
  $ hg drop -r 0
  abort: root changeset cannot be dropped
  [255]

  $ hg log -G -T '{rev} {desc|firstline}'
  o  0 r0
  
RESET and SETUP
  $ reset
  $ cat >> .hg/hgrc <<EOF
  > [extensions]
  > rebase=
  > drop=
  > [experimental]
  > evolution=all
  > EOF

TEST: dropping changeset in the middle of the stack
  $ hg debugbuilddag +4 -m
  $ hg log -G -T '{rev} {desc|firstline}'
  o  3 r3
  |
  o  2 r2
  |
  o  1 r1
  |
  o  0 r0
  
  $ hg drop -r 2
  Dropping changeset c175ba: r2
  rebasing 3:c034855f2b01 "r3" (tip)
  merging mf
  $ hg log -G -T '{rev} {desc|firstline}'
  o  4 r3
  |
  o  1 r1
  |
  o  0 r0
  
TEST: abort when more than one revision provided
  $ hg drop -r 1 4
  abort: only one revision can be dropped at a time
  [255]

RESET and SETUP
  $ reset
  $ cat >> .hg/hgrc <<EOF
  > [extensions]
  > rebase=
  > drop=
  > [experimental]
  > evolution=all
  > EOF

TEST: dropping a changest with child changesets
  $ hg debugbuilddag -m "+5 *3 +2"
  $ hg log -G -T '{rev} {desc|firstline}'
  o  7 r7
  |
  o  6 r6
  |
  o  5 r5
  |
  | o  4 r4
  | |
  | o  3 r3
  |/
  o  2 r2
  |
  o  1 r1
  |
  o  0 r0
  
  $ hg drop 2
  Dropping changeset 37d4c1: r2
  rebasing 3:a422badec216 "r3"
  merging mf
  rebasing 4:b762560d23fd "r4"
  merging mf
  rebasing 5:e76b6544a13a "r5"
  merging mf
  rebasing 6:4905937520ff "r6"
  merging mf
  rebasing 7:2c7cfba83429 "r7" (tip)
  merging mf
  $ hg log -G -T '{rev} {desc|firstline}'
  o  12 r7
  |
  o  11 r6
  |
  o  10 r5
  |
  | o  9 r4
  | |
  | o  8 r3
  |/
  o  1 r1
  |
  o  0 r0
  
TEST: aborting drop on merge changeset

  $ hg checkout 8
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge 12
  merging mf
  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg commit -m "merge"
  $ hg log -G -T '{rev} {desc|firstline}'
  @    13 merge
  |\
  | o  12 r7
  | |
  | o  11 r6
  | |
  | o  10 r5
  | |
  +---o  9 r4
  | |
  o |  8 r3
  |/
  o  1 r1
  |
  o  0 r0
  
  $ hg drop 13
  abort: merge changeset cannot be dropped
  [255]

TEST: abort when dropping a public changeset
  $ hg phase --public -r 1
  $ hg drop 1
  abort: public changeset which landed cannot be dropped
  [255]

RESET and SETUP
  $ reset
  $ cat >> .hg/hgrc <<EOF
  > [extensions]
  > rebase=
  > drop=
  > [experimental]
  > evolution=all
  > EOF

TEST: dropping a changeset with merge conflict
  $ hg debugbuilddag -o +4
  $ hg log -G -T '{rev} {desc|firstline}'
  o  3 r3
  |
  o  2 r2
  |
  o  1 r1
  |
  o  0 r0
  
  $ hg drop 1
  Dropping changeset 2a8ed6: r1
  rebasing 2:3d69e4d36b46 "r2"
  merging of
  warning: conflicts while merging of! (edit, then use 'hg resolve --mark')
  conflict occurred during drop: please fix it by running 'hg rebase --continue', and then re-run 'hg drop'
  unresolved conflicts (see hg resolve, then hg rebase --continue)
  [1]