Add support for comparing stderr as well

test/include/simple.sh

@@ -58,9 +58,11 @@ tf_do_subtest() {
         tf_warn "bad header format";
         return $TF_ES_QUIT
     fi
-    local tcmd="tail -n+$start_at $name | $env $cmd - > $name.result"
+    touch $name.stderr.oracle
+    local tcmd="tail -n+$start_at $name | $env $cmd - > $name.stdout.result 2> $name.stderr.result"
     eval "$tcmd"
-    diff -u $name.oracle $name.result
+    diff -u $name.stdout.oracle $name.stdout.result || return $TF_ES_FAIL
+    diff -u $name.stderr.oracle $name.stderr.result || return $TF_ES_FAIL
 }
 
 tf_do_subtests() {