Merge branch 'ra/t3600-test-path-funcs'

A GSoC micro.

* ra/t3600-test-path-funcs:
  t3600: use helpers to replace test -d/f/e/s <path>
  t3600: modernize style
  test functions: add function `test_file_not_empty`

t/test-lib-functions.sh

@@ -593,6 +593,15 @@ test_dir_is_empty () {
 	fi
 }
 
+# Check if the file exists and has a size greater than zero
+test_file_not_empty () {
+	if ! test -s "$1"
+	then
+		echo "'$1' is not a non-empty file."
+		false
+	fi
+}
+
 test_path_is_missing () {
 	if test -e "$1"
 	then