cli.test: failing test on stdin manifest

behavior ought to be, when `-f <file>` is not provided, then expect the
manifest to be provided on stdin.
Currently gomtree just fails if there is no `-f` (and it is not `-c`)

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

test/cli/0008.sh

@@ -0,0 +1,22 @@
+#!/bin/bash
+set -e
+
+name=$(basename $0)
+root="$(dirname $(dirname $(dirname $0)))"
+gomtree=$(readlink -f ${root}/gomtree)
+t=$(mktemp -d /tmp/go-mtree.XXXXXX)
+
+echo "[${name}] Running in ${t}"
+
+pushd ${root}
+mkdir -p ${t}/extract
+git archive --format=tar HEAD^{tree} . | tar -C ${t}/extract/ -x
+
+${gomtree} -K sha256digest -c -p ${t}/extract/ > ${t}/${name}.mtree
+
+## This is a use-case for checking a directory, but by reading the manifest from stdin
+## since the `-f` flag is not provided.
+cat ${t}/${name}.mtree | ${gomtree} -p ${t}/extract/
+
+popd
+rm -rf ${t}