Add an external tool tester

This will collect example outputs of externals tools that Liquidprompt
uses, so that we can build integration tests for these tools.

This does not include VCS providers, since without a repository, most of
the commands will simply error out. Deeper integration tests will need
to be written for VCS providers. And while most of these tools here are
packaged with an OS and therefore are OS version dependent, VCS
providers are often updated to the latest version regardless of OS.

tools/external-tool-tester.sh

@@ -0,0 +1,64 @@
+#!/bin/sh
+
+# Do NOT error on failed commands
+set +e
+
+test_tool() {
+  local stderr
+  printf '\nCommand: "%s"\n--------stdout--------\n' "$*"
+  { stderr="$( { "$@"; } 2>&1 1>&3 3>&- )"; } 3>&1
+  printf '\n--------stderr--------\n%s\n----------------------\nReturn code: "%s"\n' "$stderr" "$?"
+}
+
+# Export needed variables
+export LC_ALL=C
+
+# Print uname
+printf 'Uname:\n'
+uname -a
+
+test_tool uname
+
+hostname_cksum() {
+  hostname | cksum
+}
+test_tool hostname_cksum
+
+test_tool tput sgr0
+test_tool tput me
+test_tool tput bold
+test_tool tput md
+test_tool tput smul
+test_tool tput us
+test_tool tput colors
+test_tool tput setaf 0
+test_tool tput AF 0
+test_tool tput AF 0 0 0
+test_tool tput setab 0
+test_tool tput AB 0
+test_tool tput AB 0 0 0
+
+test_tool who am i
+test_tool ps -o comm= -p "$PPID"
+test_tool logname
+
+test_tool screen -ls
+test_tool tmux list-sessions
+
+test_tool acpi --battery
+test_tool pmset -g batt
+
+test_tool nproc
+# Not actually a command used, we read directly from the file
+test_tool cat /proc/loadavg
+test_tool sysctl -n hw.ncpu
+test_tool sysctl -n vm.loadavg
+test_tool kstat -m cpu_info
+test_tool uptime
+
+test_tool sensors -u
+test_tool acpi -t
+
+test_tool date '+%I %M'
+test_tool tty
+test_tool basename -- /dev/pts/0