view tests/test-rename.t @ 42044:bb271ec2fbfb

compression: introduce a `storage.revlog.zstd.level` configuration

This option control the zstd compression level used when compressing revlog
chunk. The usage of zstd for revlog compression has not graduated from
experimental yet, but we intend to fix that soon.

The option name for the compression level is more straight forward to pick, so
this changesets comes first.  Having a dedicated option for each compression
engine is useful because they don't support the same range of values.

I ran the same measurement as for the zlib compression level (in the parent
changesets). The variation in repository size is stay mostly in the same (small)
range. The "read/write" performance see smallish variation, but are overall much
better than zlib. Write performance show the same tend of having better write
performance for when reaching high-end compression.

Again, we don't intend to change the default zstd compression level (currently:
3) in this series. However this is worth investigating in the future.

The Performance comparison of zlib vs zstd is quite impressive. The repository
size stay in the same range, but the performance are much better in all
situations.

Comparison summary
==================

We are looking at:
- performance range for zlib
- performance range for zstd
- comparison of default zstd (level-3) to default zlib (level 6)
- comparison of the slowest zstd time to the fastest zlib time

Read performance:
-----------------
          |           zlib          |           zstd          | cmp | f2s
mercurial |   0.170159 -   0.189219 |   0.144127 -   0.149624 | 80% | 88%
pypy      |   2.679217 -   2.768691 |   1.532317 -   1.705044 | 60% | 63%
netbeans  | 122.477027 - 141.620281 |  72.996346 -  89.731560 | 58% | 73%
mozilla   | 147.867662 - 170.572118 |  91.700995 - 105.853099 | 56% | 71%

Write performance:
------------------
          |           zlib          |           zstd          | cmp | f2s
mercurial |  53.250304 - 56.2936129 |  40.877025 -  45.677286 | 75% | 86%
pypy      | 460.721984 - 476.589918 | 270.545409 - 301.002219 | 63% | 65%
netbeans  | 520.560316 - 715.930400 | 370.356311 - 428.329652 | 55% | 82%
mozilla   | 739.803002 - 987.056093 | 505.152906 - 591.930683 | 57% | 80%

Raw data
--------

repo      alg lvl  .hg/store size  00manifest.d read       write

mercurial zlib  1      49,402,813     5,963,475   0.170159  53.250304
mercurial zlib  6      47,197,397     5,875,730   0.182820  56.264320
mercurial zlib  9      47,121,596     5,849,781   0.189219  56.293612

mercurial zstd  1      49,737,084     5,966,355   0.144127  40.877025
mercurial zstd  3      48,961,867     5,895,208   0.146376  42.268142
mercurial zstd  5      48,200,592     5,938,676   0.149624  43.162875
mercurial zstd 10      47,833,520     5,913,353   0.145185  44.012489
mercurial zstd 15      47,314,604     5,728,679   0.147686  45.677286
mercurial zstd 20      47,330,502     5,830,539   0.145789  45.025407
mercurial zstd 22      47,330,076     5,830,539   0.143996  44.690460


pypy      zlib  1     370,830,572    28,462,425   2.679217 460.721984
pypy      zlib  6     340,112,317    27,648,747   2.768691 467.537158
pypy      zlib  9     338,360,736    27,639,003   2.763495 476.589918

pypy      zstd  1     362,377,479    27,916,214   1.532317 270.545409
pypy      zstd  3     354,137,693    27,905,988   1.686718 294.951509
pypy      zstd  5     342,640,043    27,655,774   1.705044 301.002219
pypy      zstd 10     334,224,327    27,164,493   1.567287 285.186239
pypy      zstd 15     329,000,363    26,645,965   1.637729 299.561332
pypy      zstd 20     324,534,039    26,199,547   1.526813 302.149827
pypy      zstd 22     324,530,595    26,198,932   1.525718 307.821218


netbeans  zlib  1   1,281,847,810   165,495,457 122.477027 520.560316
netbeans  zlib  6   1,205,284,353   159,161,207 139.876147 715.930400
netbeans  zlib  9   1,197,135,671   155,034,586 141.620281 678.297064

netbeans  zstd  1   1,259,581,737   160,840,613  72.996346 370.356311
netbeans  zstd  3   1,232,978,122   157,691,551  81.622317 396.733087
netbeans  zstd  5   1,208,034,075   160,246,880  83.080549 364.342626
netbeans  zstd 10   1,188,624,176   156,083,417  79.323935 403.594602
netbeans  zstd 15   1,176,973,589   153,859,477  89.731560 428.329652
netbeans  zstd 20   1,162,958,258   151,147,535  82.842667 392.335349
netbeans  zstd 22   1,162,707,029   151,150,220  82.565695 402.840655


mozilla   zlib  1   2,775,497,186   298,527,987 147.867662 751.263721
mozilla   zlib  6   2,596,856,420   286,597,671 170.572118 987.056093
mozilla   zlib  9   2,587,542,494   287,018,264 163.622338 739.803002

mozilla   zstd  1   2,723,159,348   286,617,532  91.700995 570.042751
mozilla   zstd  3   2,665,055,001   286,152,013  95.240155 561.412805
mozilla   zstd  5   2,607,819,817   288,060,030 101.978048 505.152906
mozilla   zstd 10   2,558,761,085   283,967,648 104.113481 497.771202
mozilla   zstd 15   2,526,216,060   275,581,300 105.853099 591.930683
mozilla   zstd 20   2,485,114,806   266,478,859  95.268795 576.515389
mozilla   zstd 22   2,484,869,080   266,456,505  94.429282 572.785537

  $ hg init
  $ mkdir d1 d1/d11 d2
  $ echo d1/a > d1/a
  $ echo d1/ba > d1/ba
  $ echo d1/a1 > d1/d11/a1
  $ echo d1/b > d1/b
  $ echo d2/b > d2/b
  $ hg add d1/a d1/b d1/ba d1/d11/a1 d2/b
  $ hg commit -m "1"

rename a single file

  $ hg rename d1/d11/a1 d2/c
  $ hg --config ui.portablefilenames=abort rename d1/a d1/con.xml
  abort: filename contains 'con', which is reserved on Windows: d1/con.xml
  [255]
  $ hg sum
  parent: 0:9b4b6e7b2c26 tip
   1
  branch: default
  commit: 1 renamed
  update: (current)
  phases: 1 draft
  $ hg status -C
  A d2/c
    d1/d11/a1
  R d1/d11/a1
  $ hg update -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm d2/c

rename a single file using absolute paths

  $ hg rename `pwd`/d1/d11/a1 `pwd`/d2/c
  $ hg status -C
  A d2/c
    d1/d11/a1
  R d1/d11/a1
  $ hg update -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm d2/c

rename --after a single file

  $ mv d1/d11/a1 d2/c
  $ hg rename --after d1/d11/a1 d2/c
  $ hg status -C
  A d2/c
    d1/d11/a1
  R d1/d11/a1
  $ hg update -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm d2/c

rename --after a single file when src and tgt already tracked

  $ mv d1/d11/a1 d2/c
  $ hg addrem -s 0
  removing d1/d11/a1
  adding d2/c
  $ hg rename --after d1/d11/a1 d2/c
  $ hg status -C
  A d2/c
    d1/d11/a1
  R d1/d11/a1
  $ hg update -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm d2/c

rename --after a single file to a nonexistent target filename

  $ hg rename --after d1/a dummy
  d1/a: not recording move - dummy does not exist
  [1]

move a single file to an existing directory

  $ hg rename d1/d11/a1 d2
  $ hg status -C
  A d2/a1
    d1/d11/a1
  R d1/d11/a1
  $ hg update -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm d2/a1

move --after a single file to an existing directory

  $ mv d1/d11/a1 d2
  $ hg rename --after d1/d11/a1 d2
  $ hg status -C
  A d2/a1
    d1/d11/a1
  R d1/d11/a1
  $ hg update -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm d2/a1

rename a file using a relative path

  $ (cd d1/d11; hg rename ../../d2/b e)
  $ hg status -C
  A d1/d11/e
    d2/b
  R d2/b
  $ hg update -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm d1/d11/e

rename --after a file using a relative path

  $ (cd d1/d11; mv ../../d2/b e; hg rename --after ../../d2/b e)
  $ hg status -C
  A d1/d11/e
    d2/b
  R d2/b
  $ hg update -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm d1/d11/e

rename directory d1 as d3

  $ hg rename d1/ d3
  moving d1/a to d3/a
  moving d1/b to d3/b
  moving d1/ba to d3/ba
  moving d1/d11/a1 to d3/d11/a1
  $ hg status -C
  A d3/a
    d1/a
  A d3/b
    d1/b
  A d3/ba
    d1/ba
  A d3/d11/a1
    d1/d11/a1
  R d1/a
  R d1/b
  R d1/ba
  R d1/d11/a1
  $ hg update -C
  4 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm -rf d3

rename --after directory d1 as d3

  $ mv d1 d3
  $ hg rename --after d1 d3
  moving d1/a to d3/a
  moving d1/b to d3/b
  moving d1/ba to d3/ba
  moving d1/d11/a1 to d3/d11/a1
  $ hg status -C
  A d3/a
    d1/a
  A d3/b
    d1/b
  A d3/ba
    d1/ba
  A d3/d11/a1
    d1/d11/a1
  R d1/a
  R d1/b
  R d1/ba
  R d1/d11/a1
  $ hg update -C
  4 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm -rf d3

move a directory using a relative path

  $ (cd d2; mkdir d3; hg rename ../d1/d11 d3)
  moving ../d1/d11/a1 to d3/d11/a1
  $ hg status -C
  A d2/d3/d11/a1
    d1/d11/a1
  R d1/d11/a1
  $ hg update -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm -rf d2/d3

move --after a directory using a relative path

  $ (cd d2; mkdir d3; mv ../d1/d11 d3; hg rename --after ../d1/d11 d3)
  moving ../d1/d11/a1 to d3/d11/a1
  $ hg status -C
  A d2/d3/d11/a1
    d1/d11/a1
  R d1/d11/a1
  $ hg update -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm -rf d2/d3

move directory d1/d11 to an existing directory d2 (removes empty d1)

  $ hg rename d1/d11/ d2
  moving d1/d11/a1 to d2/d11/a1
  $ hg status -C
  A d2/d11/a1
    d1/d11/a1
  R d1/d11/a1
  $ hg update -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm -rf d2/d11

move directories d1 and d2 to a new directory d3

  $ mkdir d3
  $ hg rename d1 d2 d3
  moving d1/a to d3/d1/a
  moving d1/b to d3/d1/b
  moving d1/ba to d3/d1/ba
  moving d1/d11/a1 to d3/d1/d11/a1
  moving d2/b to d3/d2/b
  $ hg status -C
  A d3/d1/a
    d1/a
  A d3/d1/b
    d1/b
  A d3/d1/ba
    d1/ba
  A d3/d1/d11/a1
    d1/d11/a1
  A d3/d2/b
    d2/b
  R d1/a
  R d1/b
  R d1/ba
  R d1/d11/a1
  R d2/b
  $ hg update -C
  5 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm -rf d3

move --after directories d1 and d2 to a new directory d3

  $ mkdir d3
  $ mv d1 d2 d3
  $ hg rename --after d1 d2 d3
  moving d1/a to d3/d1/a
  moving d1/b to d3/d1/b
  moving d1/ba to d3/d1/ba
  moving d1/d11/a1 to d3/d1/d11/a1
  moving d2/b to d3/d2/b
  $ hg status -C
  A d3/d1/a
    d1/a
  A d3/d1/b
    d1/b
  A d3/d1/ba
    d1/ba
  A d3/d1/d11/a1
    d1/d11/a1
  A d3/d2/b
    d2/b
  R d1/a
  R d1/b
  R d1/ba
  R d1/d11/a1
  R d2/b
  $ hg update -C
  5 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm -rf d3

move everything under directory d1 to existing directory d2, do not
overwrite existing files (d2/b)

  $ hg rename d1/* d2
  d2/b: not overwriting - file already committed
  ('hg rename --force' to replace the file by recording a rename)
  moving d1/d11/a1 to d2/d11/a1
  [1]
  $ hg status -C
  A d2/a
    d1/a
  A d2/ba
    d1/ba
  A d2/d11/a1
    d1/d11/a1
  R d1/a
  R d1/ba
  R d1/d11/a1
  $ diff -u d1/b d2/b
  --- d1/b	* (glob)
  +++ d2/b	* (glob)
  @@ * (glob)
  -d1/b
  +d2/b
  [1]
  $ hg update -C
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm d2/a d2/ba d2/d11/a1

attempt to move one file into a non-existent directory

  $ hg rename d1/a dx/
  abort: destination dx/ is not a directory
  [255]
  $ hg status -C
  $ hg update -C
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved

attempt to move potentially more than one file into a non-existent directory

  $ hg rename 'glob:d1/**' dx
  abort: with multiple sources, destination must be an existing directory
  [255]

move every file under d1 to d2/d21

  $ mkdir d2/d21
  $ hg rename 'glob:d1/**' d2/d21
  moving d1/a to d2/d21/a
  moving d1/b to d2/d21/b
  moving d1/ba to d2/d21/ba
  moving d1/d11/a1 to d2/d21/a1
  $ hg status -C
  A d2/d21/a
    d1/a
  A d2/d21/a1
    d1/d11/a1
  A d2/d21/b
    d1/b
  A d2/d21/ba
    d1/ba
  R d1/a
  R d1/b
  R d1/ba
  R d1/d11/a1
  $ hg update -C
  4 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm -rf d2/d21

move --after some files under d1 to d2/d21

  $ mkdir d2/d21
  $ mv d1/a d1/d11/a1 d2/d21
  $ hg rename --after 'glob:d1/**' d2/d21
  moving d1/a to d2/d21/a
  d1/b: not recording move - d2/d21/b does not exist
  d1/ba: not recording move - d2/d21/ba does not exist
  moving d1/d11/a1 to d2/d21/a1
  [1]
  $ hg status -C
  A d2/d21/a
    d1/a
  A d2/d21/a1
    d1/d11/a1
  R d1/a
  R d1/d11/a1
  $ hg update -C
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm -rf d2/d21

move every file under d1 starting with an 'a' to d2/d21 (regexp)

  $ mkdir d2/d21
  $ hg rename 're:d1/([^a][^/]*/)*a.*' d2/d21
  moving d1/a to d2/d21/a
  moving d1/d11/a1 to d2/d21/a1
  $ hg status -C
  A d2/d21/a
    d1/a
  A d2/d21/a1
    d1/d11/a1
  R d1/a
  R d1/d11/a1
  $ hg update -C
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm -rf d2/d21

attempt to overwrite an existing file

  $ echo "ca" > d1/ca
  $ hg rename d1/ba d1/ca
  d1/ca: not overwriting - file exists
  ('hg rename --after' to record the rename)
  [1]
  $ hg status -C
  ? d1/ca
  $ hg update -C
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved

forced overwrite of an existing file

  $ echo "ca" > d1/ca
  $ hg rename --force d1/ba d1/ca
  $ hg status -C
  A d1/ca
    d1/ba
  R d1/ba
  $ hg update -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm d1/ca

attempt to overwrite an existing broken symlink

#if symlink
  $ ln -s ba d1/ca
  $ hg rename --traceback d1/ba d1/ca
  d1/ca: not overwriting - file exists
  ('hg rename --after' to record the rename)
  [1]
  $ hg status -C
  ? d1/ca
  $ hg update -C
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm d1/ca

replace a symlink with a file

  $ ln -s ba d1/ca
  $ hg rename --force d1/ba d1/ca
  $ hg status -C
  A d1/ca
    d1/ba
  R d1/ba
  $ hg update -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm d1/ca
#endif

do not copy more than one source file to the same destination file

  $ mkdir d3
  $ hg rename d1/* d2/* d3
  moving d1/d11/a1 to d3/d11/a1
  d3/b: not overwriting - d2/b collides with d1/b
  [1]
  $ hg status -C
  A d3/a
    d1/a
  A d3/b
    d1/b
  A d3/ba
    d1/ba
  A d3/d11/a1
    d1/d11/a1
  R d1/a
  R d1/b
  R d1/ba
  R d1/d11/a1
  $ hg update -C
  4 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm -rf d3

move a whole subtree with "hg rename ."

  $ mkdir d3
  $ (cd d1; hg rename . ../d3)
  moving a to ../d3/d1/a
  moving b to ../d3/d1/b
  moving ba to ../d3/d1/ba
  moving d11/a1 to ../d3/d1/d11/a1
  $ hg status -C
  A d3/d1/a
    d1/a
  A d3/d1/b
    d1/b
  A d3/d1/ba
    d1/ba
  A d3/d1/d11/a1
    d1/d11/a1
  R d1/a
  R d1/b
  R d1/ba
  R d1/d11/a1
  $ hg update -C
  4 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm -rf d3

move a whole subtree with "hg rename --after ."

  $ mkdir d3
  $ mv d1/* d3
  $ (cd d1; hg rename --after . ../d3)
  moving a to ../d3/a
  moving b to ../d3/b
  moving ba to ../d3/ba
  moving d11/a1 to ../d3/d11/a1
  $ hg status -C
  A d3/a
    d1/a
  A d3/b
    d1/b
  A d3/ba
    d1/ba
  A d3/d11/a1
    d1/d11/a1
  R d1/a
  R d1/b
  R d1/ba
  R d1/d11/a1
  $ hg update -C
  4 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm -rf d3

move the parent tree with "hg rename .."

  $ (cd d1/d11; hg rename .. ../../d3)
  moving ../a to ../../d3/a
  moving ../b to ../../d3/b
  moving ../ba to ../../d3/ba
  moving a1 to ../../d3/d11/a1
  $ hg status -C
  A d3/a
    d1/a
  A d3/b
    d1/b
  A d3/ba
    d1/ba
  A d3/d11/a1
    d1/d11/a1
  R d1/a
  R d1/b
  R d1/ba
  R d1/d11/a1
  $ hg update -C
  4 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm -rf d3

skip removed files

  $ hg remove d1/b
  $ hg rename d1 d3
  moving d1/a to d3/a
  moving d1/ba to d3/ba
  moving d1/d11/a1 to d3/d11/a1
  $ hg status -C
  A d3/a
    d1/a
  A d3/ba
    d1/ba
  A d3/d11/a1
    d1/d11/a1
  R d1/a
  R d1/b
  R d1/ba
  R d1/d11/a1
  $ hg update -C
  4 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm -rf d3

transitive rename

  $ hg rename d1/b d1/bb
  $ hg rename d1/bb d1/bc
  $ hg status -C
  A d1/bc
    d1/b
  R d1/b
  $ hg update -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm d1/bc

transitive rename --after

  $ hg rename d1/b d1/bb
  $ mv d1/bb d1/bc
  $ hg rename --after d1/bb d1/bc
  $ hg status -C
  A d1/bc
    d1/b
  R d1/b
  $ hg update -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm d1/bc

  $ echo "# idempotent renames (d1/b -> d1/bb followed by d1/bb -> d1/b)"
  # idempotent renames (d1/b -> d1/bb followed by d1/bb -> d1/b)
  $ hg rename d1/b d1/bb
  $ echo "some stuff added to d1/bb" >> d1/bb
  $ hg rename d1/bb d1/b
  $ hg status -C
  M d1/b
  $ hg update -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

overwriting with renames (issue1959)

  $ hg rename d1/a d1/c
  $ hg rename d1/b d1/a
  $ hg status -C
  M d1/a
    d1/b
  A d1/c
    d1/a
  R d1/b
  $ hg diff --git
  diff --git a/d1/a b/d1/a
  --- a/d1/a
  +++ b/d1/a
  @@ -1,1 +1,1 @@
  -d1/a
  +d1/b
  diff --git a/d1/b b/d1/b
  deleted file mode 100644
  --- a/d1/b
  +++ /dev/null
  @@ -1,1 +0,0 @@
  -d1/b
  diff --git a/d1/a b/d1/c
  copy from d1/a
  copy to d1/c
  $ hg update -C
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm d1/c # The file was marked as added, so 'hg update' action  was 'forget'

check illegal path components

  $ hg rename d1/d11/a1 .hg/foo
  abort: path contains illegal component: .hg/foo
  [255]
  $ hg status -C
  $ hg rename d1/d11/a1 ../foo
  abort: ../foo not under root '$TESTTMP'
  [255]
  $ hg status -C

  $ mv d1/d11/a1 .hg/foo
  $ hg rename --after d1/d11/a1 .hg/foo
  abort: path contains illegal component: .hg/foo
  [255]
  $ hg status -C
  ! d1/d11/a1
  $ hg update -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm .hg/foo

  $ hg rename d1/d11/a1 .hg
  abort: path contains illegal component: .hg/a1
  [255]
  $ hg --config extensions.largefiles= rename d1/d11/a1 .hg
  The fsmonitor extension is incompatible with the largefiles extension and has been disabled. (fsmonitor !)
  abort: path contains illegal component: .hg/a1
  [255]
  $ hg status -C
  $ hg rename d1/d11/a1 ..
  abort: ../a1 not under root '$TESTTMP'
  [255]
  $ hg --config extensions.largefiles= rename d1/d11/a1 ..
  The fsmonitor extension is incompatible with the largefiles extension and has been disabled. (fsmonitor !)
  abort: ../a1 not under root '$TESTTMP'
  [255]
  $ hg status -C

  $ mv d1/d11/a1 .hg
  $ hg rename --after d1/d11/a1 .hg
  abort: path contains illegal component: .hg/a1
  [255]
  $ hg status -C
  ! d1/d11/a1
  $ hg update -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm .hg/a1

  $ (cd d1/d11; hg rename ../../d2/b ../../.hg/foo)
  abort: path contains illegal component: .hg/foo
  [255]
  $ hg status -C
  $ (cd d1/d11; hg rename ../../d2/b ../../../foo)
  abort: ../../../foo not under root '$TESTTMP'
  [255]
  $ hg status -C

check that stat information such as mtime is preserved on rename - it's unclear
whether the `touch` and `stat` commands are portable, so we mimic them using
python.  Not all platforms support precision of even one-second granularity, so
we allow a rather generous fudge factor here; 1234567890 is 2009, and the
primary thing we care about is that it's not the machine's current time;
hopefully it's really unlikely for a machine to have such a broken clock that
this test fails. :)

  $ mkdir mtime
Create the file (as empty), then update its mtime and atime to be 1234567890.
  >>> import os
  >>> filename = "mtime/f"
  >>> mtime = 1234567890
  >>> open(filename, "w").close()
  >>> os.utime(filename, (mtime, mtime))
  $ hg ci -qAm 'add mtime dir'
"hg cp" does not preserve the mtime, so it should be newer than the 2009
timestamp.
  $ hg cp -q mtime mtime_cp
  >>> from __future__ import print_function
  >>> import os
  >>> filename = "mtime_cp/f"
  >>> print(os.stat(filename).st_mtime < 1234567999)
  False
"hg mv" preserves the mtime, so it should be ~equal to the 2009 timestamp
(modulo some fudge factor due to not every system supporting 1s-level
precision).
  $ hg mv -q mtime mtime_mv
  >>> from __future__ import print_function
  >>> import os
  >>> filename = "mtime_mv/f"
  >>> print(os.stat(filename).st_mtime < 1234567999)
  True