Test date logic in korn shell - shell

Question

I am looking for a way to test the following korn shell date logic for different days and times. I do not have root access to change the actual date on the system.
CUR_DAY=$(TZ="US/Eastern" date +%a)
typeset -i CUR_HOUR=$(TZ="US/Eastern" date +%H)
# Set the start and end hour given in eastern time
typeset -i START_HOUR=22
typeset -i END_HOUR=7
case $CUR_DAY in
Sun)
if [[ $CUR_HOUR -ge $START_HOUR ]]
then
echo "Send message1"
fi;;
Mon|Tue|Wed|Thu)
if [[ $CUR_HOUR -ge $START_HOUR || $CUR_HOUR -lt $END_HOUR ]]
then
echo "Send message2"
fi;;
Fri)
if [[ "$CUR_HOUR" -lt $END_HOUR ]]
then
echo "Send message3"
fi;;
esac

Answer 1

If you want to test just the logic (and not that date is working correctly), then allow your script to accept CUR_DAY and CUR_HOUR as arguments or via the environment, instead of always running date.
Via the environment (CUR_DAY=9 CUR_HOUR=22 myscript)
: ${CUR_DAY:=$(date +%a)}
: ${CUR_HOUR:=$(date +%H)}
Via arguments (myscript 9 22)
CUR_DAY=${1:-$(date +%a)}
CUR_HOUR=${2:-$(date +%H)}
Either approach will work in any POSIX-compliant shell.

Answer 2

The easiest way to test this is to conditionally add the -d argument to date (assuming the GNU implementation) to pass it a specific date and time for which you intend to test the function's behavior.
The below passes arguments straight through to date, allowing the invocation to be adapted as appropriate:
check_dates() {
typeset cur_day cur_hour start_hour end_hour
# call external date command only once to minimize external process overhead
read -r cur_day cur_hour < <(TZ="US/Eastern" date "$#" +'%a %H')
# trim leading 0s -- otherwise, values will be seen as octal when performing math
cur_day=${cur_day#0}; cur_hour=${cur_hour#0}
start_hour=22
end_hour=8
case $cur_day in
Sun)
if (( cur_hour <= start_hour )); then
echo "Send message1"
fi
;;
Mon|Tue|Wed|Thu)
if (( cur_hour >= start_hour )) || (( cur_hour < end_hour )); then
echo "Send message2"
fi
;;
Fri)
if (( cur_hour < end_hour )); then
echo "Send message3"
fi
;;
esac
}
Thereafter:
check_dates # check for current date and time
check_dates -d '2015-01-06 03:00:00 UTC' # check for a specific date and time
If you're inclined not to use "$#", and don't mind hardcoding behavior specific to GNU date, consider:
check_dates() {
typeset cur_day cur_hour for_date
for_date=$1
read -r cur_day cur_hour < <(TZ="US/Eastern" date ${for_date:+ -d "$for_date"} +'%a %H')
...
}
...which passes -d "$for_date" only if for_date is set to a non-empty value.