tests: add test for backing files creation

Basic test that checks that create-backingfiles.sh does not fail
for many combination of disk images.
Does not check that the created images are actually valid.

tests/create-backingfiles-test.sh

@@ -0,0 +1,80 @@
+#!/bin/bash
+
+if [[ $EUID -ne 0 ]]
+then
+  echo "STOP: Run this script as root."
+  exit 1
+fi
+
+if [ "$(systemd-detect-virt)" == "none" ]
+then
+  echo "WARNING, it is recommended to run this script in a VM."
+  echo "Press enter to continue, or ctrl-c to abort."
+  read
+fi
+
+BACKINGFILES_FOLDER=$(mktemp -d backingfilestestXXX)
+LOG="$BACKINGFILES_FOLDER-log.txt"
+
+function checksuccess {
+  name=$(printf '%6s %6s %6s %6s %6s' "$1" "$2" "$3" "$4" "$6")
+  if ../setup/pi/create-backingfiles.sh "$@"
+  then
+    printf '%-45s %s\n' "$name" OK
+    printf '%-45s %s\n' "$name" OK > /dev/tty
+  else
+    printf '%-45s %s\n' "$name" FAIL
+    printf '%-45s %s\n' "$name" FAIL > /dev/tty
+    SUCCESS=false
+  fi
+}
+
+SUCCESS=true
+
+FALLOCATE=$(which fallocate)
+
+function fallocate {
+  if [ "$1" != "-l" ]
+  then
+    echo "Can't emulate fallocate invocation with args " "$@"
+    exit 1
+  fi
+  truncate -s "$2" "$3"
+}
+
+if ! $FALLOCATE -l 1M "$BACKINGFILES_FOLDER/test.bin"
+then
+  echo "emulating fallocate using truncate"
+  export -f fallocate
+fi
+rm "$BACKINGFILES_FOLDER/test.bin"
+
+{
+  for cam in 30G 40G
+  do
+    for music in 0 4G
+    do
+      for lightshow in 0 100M 1G
+      do
+        for boombox in 0 100M
+        do
+          for exfat in true false
+          do
+            checksuccess "$cam" "$music" "$lightshow" "$boombox" "$BACKINGFILES_FOLDER" "$exfat" < /dev/null
+	    find "$BACKINGFILES_FOLDER" -type f | xargs rm
+          done
+        done
+      done
+    done
+  done
+
+
+} &>> "$LOG"
+
+if [ "$SUCCESS" = "true" ]
+then
+  rm -rf "$BACKINGFILES_FOLDER" "$LOG"
+else
+  echo "One or more tests failed, see $LOG for details."
+  exit 1
+fi