Issue 2691 QC test failure for betweenLinesPS

Title QC test failure for betweenLinesPS
Priority bug Status resolved
Milestone Resolved in
Superseder Nosy List bfrk
Assigned To

Created on 2022-04-22.12:47:35 by bfrk, last changed 2022-06-07.07:39:37 by bfrk.

msg22993 (view) Author: bfrk Date: 2022-04-22.12:47:33
ben@home[1]:.../darcs/screened>cabal run darcs-test -- -j4 -s=u -
q=10000 -t betweenLinesPS -r=-4849332720703066203
Up to date
Using darcs executable in /home/ben/src/darcs/screened/dist-
Locale encoding is UTF-8
    betweenLinesPS behaves like its spec: [Failed]
*** Failed! Falsified (after 5306 tests):
(used seed -4849332720703066203)

         Properties  Total      
 Passed  0           0          
 Failed  1           1          
 Total   1           1          

I am not sure what the precise precondition is but I guess it hardly 
matters: betweenLinesPS is obviously only meant to work for start/end 
*lines* IOW non-empty ByteStrings w/o any newlines in them. Indeed, 
strenghtening the precondition in this way rules out the above test 
case and seems to work, so I'll go for that. And document the 
precondition in the haddocks.
msg22994 (view) Author: bfrk Date: 2022-04-23.15:04:09
It turned out this QC test is almost worthless because with the given 
test case distribution the probability that the call to betweenLinesPS 
succeeds is practically zero. One way to improve the test is to choose 
characters from a (much) smaller set: with only ['a','b','\n'] allowed, 
we have at least a 6% chance that the arbitrary start and end lines 
actually appear (in order, i.e. first start, then end). This change 
quickly uncovered actual bugs in the implementation! Indeed, if the 
start or end line appears in the input but not as a complete line but 
rather as the end of an existing line, betweenLinesPS fails instead of 
searching further for a complete line.
msg23008 (view) Author: bfrk Date: 2022-06-07.07:39:36
See patch2237
Date User Action Args
2022-04-22 12:47:35bfrkcreate
2022-04-23 15:04:09bfrksetmessages: + msg22994
2022-06-07 07:39:37bfrksetstatus: unknown -> resolved
priority: bug
messages: + msg23008