refute_output without args asserts output is empty

src/assert.bash

diff --git a/src/assert.bash b/src/assert.bash
index b680fad..e1ffc4b 100644
--- a/src/assert.bash
+++ b/src/assert.bash
@@ -293,9 +293,14 @@
 refute_output() {
   local -i is_mode_partial=0
   local -i is_mode_regexp=0
+  local -i is_mode_empty=0
   local -i use_stdin=0
 
   # Handle options.
+  if (( $# == 0 )); then
+    is_mode_empty=1
+  fi
+
   while (( $# > 0 )); do
     case "$1" in
       -p|--partial) is_mode_partial=1; shift ;;
@@ -329,7 +334,13 @@
   fi
 
   # Matching.
-  if (( is_mode_regexp )); then
+  if (( is_mode_empty )); then
+    if [ -n "$output" ]; then
+      echo 'expected no output, but output was non-empty' \
+      | batslib_decorate 'unexpected output' \
+      | fail
+    fi
+  elif (( is_mode_regexp )); then
     if [[ $output =~ $unexpected ]] || (( $? == 0 )); then
       batslib_print_kv_single_or_multi 6 \
           'regexp'  "$unexpected" \

test/50-assert-16-refute_output.bats

diff --git a/test/50-assert-16-refute_output.bats b/test/50-assert-16-refute_output.bats
index a289717..7983750 100755
--- a/test/50-assert-16-refute_output.bats
+++ b/test/50-assert-16-refute_output.bats
@@ -25,6 +25,25 @@
   [ "${lines[2]}" == '--' ]
 }
 
+@test 'refute_output(): succeeds if output is empty' {
+  run echo ''
+  run refute_output
+echo "$output"
+  [ "$status" -eq 0 ]
+  [ "${#lines[@]}" -eq 0 ]
+}
+
+@test 'refute_output(): fails if output is non-empty' {
+  run echo 'a'
+  run refute_output
+echo "$output"
+  [ "$status" -eq 1 ]
+  [ "${#lines[@]}" -eq 3 ]
+  [ "${lines[0]}" == '-- unexpected output --' ]
+  [ "${lines[1]}" == 'expected no output, but output was non-empty' ]
+  [ "${lines[2]}" == '--' ]
+}
+
 @test 'refute_output() - : reads <unexpected> from STDIN' {
   run echo '-'
   run refute_output - <<INPUT