is-globstar: native bash solution, grep solution had weird behaviour

add tests

commands/is-globstar

@@ -1,13 +1,38 @@
 #!/usr/bin/env bash
 
+function is_globstar_test() (
+	source "$DOROTHY/sources/bash.bash"
+	echo-segment --h1="TEST: $0"
+
+	eval-tester --name='empty' --status=1 \
+		-- is-globstar
+
+	eval-tester --name='empty string' --status=1 \
+		-- is-globstar ''
+
+	eval-tester --name='non-globstar string' --status=1 \
+		-- is-globstar ' /Users/runner/.cache/dorothy/unziptar/5241/rg'
+
+	eval-tester --name='star string' --status=1 \
+		-- is-globstar ' /Users/runner/.cache/dorothy/*/unziptar/5241/rg'
+
+	eval-tester --name='globstar string' --status=0 \
+		-- is-globstar ' /Users/runner/.cache/dorothy/**/unziptar/5241/rg'
+
+	echo-segment --g1="TEST: $0"
+	return 0
+)
 function is_globstar() (
 	source "$DOROTHY/sources/bash.bash"
 
-	# https://stackoverflow.com/a/240181
-	grep --quiet --fixed-strings --regexp='**' <<<"$*"
+	[[ $* == *'**'* ]]
 )
 
 # fire if invoked standalone
 if test "$0" = "${BASH_SOURCE[0]}"; then
-	is_globstar "$@"
+	if test "$*" = '--test'; then
+		is_globstar_test
+	else
+		is_globstar "$@"
+	fi
 fi