d-test.sh

#!/usr/bin/env bash
echo $BASH_VERSION ;date -R
echo 'USAGE: d-test.sh "[path/datediff.sh]" "[month..]" "[day..]"' >&2
export DEBUG=2


src="$HOME/bin/datediff.sh"
[[ -e $1 ]] && {    src="$1" ;set -- "${@:2}" ;}
echo ". $src" >&2
. "$src" -D >&2  #flag -D disables package `date' warping


for y in  1988  1989  #there should be a year in between!
do  for m in ${1:-1 2 3  6  11 12}
    do  echo "MONTH=$m"
        for d in ${2:-1 2 3   27 28 29 30 31}
        do  for h in 0 1  12  23
            do  for min in 0 1  59
                do  for s in 0 1  59
                    do
    (( d <= $(month_maxday $m $y) )) || continue
    D1="$y-$m-${d}T$h:$min:$s+00:00"
    #dates must have time zone, even if set to +00:00

        for Y in 1989 1988
        do  for M in 1 2 3  5  10 12
            do  for D in 1 2 3 4  27 28 29 30 31
                do  for H in 0 1    23
                    do  for MIN in 0 1  58
                        do  for S in 0 1  58
                            do
            (( D <= $(month_maxday $M $Y) )) || continue
            D2="$Y-$M-${D}T$H:$MIN:$S+00:00"

            {
                p=$(mainf "$D1" "$D2") || { echo >&2 ;echo "$p" ;}
            } &
            printf '\033[2K%s | %s\t(%d) [%d] {%d}\r' "${D1:0:19}" "${D2:0:19}" $((++n)) $SECONDS $((n/(SECONDS+1))) >&2
                            done
                        done
                    done
                done
            done
        done
                    done
                done
            done
        done
    done
    wait
    echo "n=$n ($y)"
done
wait
echo "N=$n"

#NOTES
#Year 1988==4405104; Year 1989==4304988; total==8.710.092
#2*6*8*4*3*3 * 9*3*3*3*2*6 == 10077696

#Note input dates must have time zone, even if set to +00:00, to avoid
#debug checkign errors as `date' programme has got undefined behaviour
#interpreting dates without timezone settings!

#LOG
##v0.16.6
#Compound range testing:
#.35171, about 35% of errors detected in testing are `datediff' only errs (9720/27644).
#.1554,  about 16% of errors is from wrong shell arithmetics compensation for start-and-end-of-month days.
#.10577, about 11% of error testing results are due to shell arithmetics outputting negative days.
#.04720, at least 5% of other times we are probably right, too, as well as `datediff' (different ways of counting).
#
##v0.16.7    (addon2)
#.4570, about 45% of errors detected in testing are `datediff' only errs (12636/27644) (compound range).
#Result differences remain the same, we detect false-positive errors thanks to addon2 code.
#It fixes most negative day ranges but takes apart a full month in these cases, which makes result more refined than `datediff' and equally correct.
#
##v0.16.8    (addon2+addon3)
#Addon3 prevents breaking a full month from count and delivers correct results, specially when dayA is `31'.
#Result differences remain the same, we detect false-positive errors thanks to addon3 code. We cannot really see bad range results any more but we note that we count differently than `datediff' in some cases.
#
#Testing was performed on 4,405,104 pairs of dates for 1988 vs. 1989 (compound range):
#.00311, `datediff' error rate is at least 3% of total dates tested.
#.006275, a 0,62% of error rate of total dates tested was produced.
#Errors are understood as results that differ from `datediff' and may be false-positive errors (just different counting refinements).
#.45709, `datediff' errs account for about 45% (12636/27644) of one testing error type (eights and nines as resulting weeks) while our results seems correct in those cases.
#.03885 `datediff' accounts for almost 4% more errs of another type (start-and-end-of-month dates), while our results seem correct in those cases.
#.4959, thus almost 50% of testing errors are only `datediff'.
#Remaining date results match although with different refinements (our results are little more refined than `datediff').