walk: directory is expected to be walked. A file is not.

Fixes: #166

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

test/cli/0011.sh

@@ -0,0 +1,22 @@
+#!/bin/bash
+set -e
+
+name=$(basename $0)
+root="$(dirname $(dirname $(dirname $0)))"
+gomtree=$(go run ${root}/test/realpath/main.go ${root}/gomtree)
+t=$(mktemp -d /tmp/go-mtree.XXXXXX)
+
+echo "[${name}] Running in ${t}"
+
+## testing comparing two files
+
+pushd ${root}
+mkdir -p ${t}/
+touch ${t}/foo
+
+## can not walk a file. We're expecting a directory.
+## https://github.com/vbatts/go-mtree/issues/166
+! ${gomtree} -c -K uname,uid,gname,gid,type,nlink,link,mode,flags,xattr,xattrs,size,time,sha256 -p ${t}/foo
+
+popd
+rm -rf ${t}