Assert/Refute against nonempty/empty output

README.md

@@ -189,12 +189,13 @@ By default, literal matching is performed. The assertion fails if
 }
 ```
 
-The expected output can be specified with a heredoc or standard input as well.
+The expected output can be specified with a heredoc or standard input as well,
+by providing `-` as an option.
 
 ```bash
 @test 'assert_output() with pipe' {
   run echo 'have'
-  echo 'want' | assert_output
+  echo 'want' | assert_output -
 }
 ```
 
@@ -210,6 +211,26 @@ actual   : have
 If either value is longer than one line both are displayed in
 *multi-line* format.
 
+#### Existence
+
+To assert that any (non-empty) output exists at all, simply omit the matching
+argument.
+
+```bash
+@test 'assert_output()' {
+  run echo 'have'
+  assert_output
+}
+```
+
+On failure, an error message is displayed.
+
+```
+-- no output --
+expected non-empty output, but output was empty
+--
+```
+
 #### Partial matching
 
 Partial matching can be enabled with the `--partial` option (`-p` for
@@ -287,12 +308,13 @@ By default, literal matching is performed. The assertion fails if
 }
 ```
 
--The unexpected output can be specified with a heredoc or standard input as well.
+The unexpected output can be specified with a heredoc or standard input as well,
+by providing `-` as an option.
 
 ```bash
 @test 'refute_output() with pipe' {
   run echo 'want'
-  echo 'want' | refute_output
+  echo 'want' | refute_output -
 }
 ```
 
@@ -307,6 +329,25 @@ output : want
 If output is longer than one line it is displayed in *multi-line*
 format.
 
+#### Existence
+
+To assert that there is no output at all, simply omit the matching argument.
+
+```bash
+@test 'refute_output()' {
+  run foo --silent
+  refute_output
+}
+```
+
+On failure, an error message is displayed.
+
+```
+-- unexpected output --
+expected no output, but output was non-empty
+--
+```
+
 #### Partial matching
 
 Partial matching can be enabled with the `--partial` option (`-p` for

src/assert.bash

@@ -185,12 +185,19 @@ assert_failure() {
 assert_output() {
   local -i is_mode_partial=0
   local -i is_mode_regexp=0
+  local -i is_mode_nonempty=0
+  local -i use_stdin=0
 
   # Handle options.
+  if (( $# == 0 )); then
+    is_mode_nonempty=1
+  fi
+
   while (( $# > 0 )); do
     case "$1" in
       -p|--partial) is_mode_partial=1; shift ;;
       -e|--regexp) is_mode_regexp=1; shift ;;
+      -) use_stdin=1; shift ;;
       --) shift; break ;;
       *) break ;;
     esac
@@ -205,17 +212,25 @@ assert_output() {
 
   # Arguments.
   local expected
-  (( $# == 0 )) && expected="$(cat -)" || expected="$1"
+  if (( use_stdin )); then
+    expected="$(cat -)"
+  else
+    expected="$1"
+  fi
 
   # Matching.
-  if (( is_mode_regexp )); then
+  if (( is_mode_nonempty )); then
+    if [ -z "$output" ]; then
+      echo 'expected non-empty output, but output was empty' \
+        | batslib_decorate 'no output' \
+        | fail
+    fi
+  elif (( is_mode_regexp )); then
     if [[ '' =~ $expected ]] || (( $? == 2 )); then
       echo "Invalid extended regular expression: \`$expected'" \
         | batslib_decorate 'ERROR: assert_output' \
         | fail
-      return $?
-    fi
-    if ! [[ $output =~ $expected ]]; then
+    elif ! [[ $output =~ $expected ]]; then
       batslib_print_kv_single_or_multi 6 \
           'regexp'  "$expected" \
           'output' "$output" \
@@ -278,12 +293,19 @@ assert_output() {
 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 ;;
       -e|--regexp) is_mode_regexp=1; shift ;;
+      -) use_stdin=1; shift ;;
       --) shift; break ;;
       *) break ;;
     esac
@@ -298,7 +320,11 @@ refute_output() {
 
   # Arguments.
   local unexpected
-  (( $# == 0 )) && unexpected="$(cat -)" || unexpected="$1"
+  if (( use_stdin )); then
+    unexpected="$(cat -)"
+  else
+    unexpected="$1"
+  fi
 
   if (( is_mode_regexp == 1 )) && [[ '' =~ $unexpected ]] || (( $? == 2 )); then
     echo "Invalid extended regular expression: \`$unexpected'" \
@@ -308,7 +334,14 @@ refute_output() {
   fi
 
   # Matching.
-  if (( is_mode_regexp )); then
+  if (( is_mode_empty )); then
+    if [ -n "$output" ]; then
+      batslib_print_kv_single_or_multi 6 \
+          'output' "$output" \
+        | batslib_decorate 'output non-empty, but expected no 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-15-assert_output.bats

@@ -26,12 +26,28 @@ load test_helper
   [ "${lines[3]}" == '--' ]
 }
 
-@test 'assert_output(): reads <expected> from STDIN' {
+@test 'assert_output(): succeeds if output is non-empty' {
   run echo 'a'
-  run assert_output <<STDIN
+  run assert_output
+  [ "$status" -eq 0 ]
+  [ "${#lines[@]}" -eq 0 ]
+}
+
+@test 'assert_output(): fails if output is empty' {
+  run echo ''
+  run assert_output
+  [ "$status" -eq 1 ]
+  [ "${#lines[@]}" -eq 3 ]
+  [ "${lines[0]}" == '-- no output --' ]
+  [ "${lines[1]}" == 'expected non-empty output, but output was empty' ]
+  [ "${lines[2]}" == '--' ]
+}
+
+@test 'assert_output() - : reads <expected> from STDIN' {
+  run echo 'a'
+  run assert_output - <<STDIN
 a
 STDIN
-echo "$output"
   [ "$status" -eq 0 ]
   [ "${#lines[@]}" -eq 0 ]
 }

test/50-assert-16-refute_output.bats

@@ -25,9 +25,26 @@ load test_helper
   [ "${lines[2]}" == '--' ]
 }
 
-@test 'refute_output(): reads <unexpected> from STDIN' {
+@test 'refute_output(): succeeds if output is empty' {
+  run echo ''
+  run refute_output
+  [ "$status" -eq 0 ]
+  [ "${#lines[@]}" -eq 0 ]
+}
+
+@test 'refute_output(): fails if output is non-empty' {
   run echo 'a'
-  run refute_output <<INPUT
+  run refute_output
+  [ "$status" -eq 1 ]
+  [ "${#lines[@]}" -eq 3 ]
+  [ "${lines[0]}" == '-- output non-empty, but expected no output --' ]
+  [ "${lines[1]}" == 'output : a' ]
+  [ "${lines[2]}" == '--' ]
+}
+
+@test 'refute_output() - : reads <unexpected> from STDIN' {
+  run echo '-'
+  run refute_output - <<INPUT
 b
 INPUT
   [ "$status" -eq 0 ]