Merge pull request #19 from jasonkarns/files

Extract assertions to separate files

10 files changed, 698 insertions, 736 deletions

diff --git a/load.bash b/load.bash
index ac4a875..14695c3 100644
--- a/load.bash
+++ b/load.bash
@@ -1 +1,29 @@
+# bats-assert - Common assertions for Bats
+#
+# Written in 2016 by Zoltan Tombol <zoltan dot tombol at gmail dot com>
+#
+# To the extent possible under law, the author(s) have dedicated all
+# copyright and related and neighboring rights to this software to the
+# public domain worldwide. This software is distributed without any
+# warranty.
+#
+# You should have received a copy of the CC0 Public Domain Dedication
+# along with this software. If not, see
+# <http://creativecommons.org/publicdomain/zero/1.0/>.
+#
+# Assertions are functions that perform a test and output relevant
+# information on failure to help debugging. They return 1 on failure
+# and 0 otherwise.
+#
+# All output is formatted for readability using the functions of
+# `output.bash' and sent to the standard error.
+
 source "$(dirname "${BASH_SOURCE[0]}")/src/assert.bash"
+source "$(dirname "${BASH_SOURCE[0]}")/src/refute.bash"
+source "$(dirname "${BASH_SOURCE[0]}")/src/assert_equal.bash"
+source "$(dirname "${BASH_SOURCE[0]}")/src/assert_success.bash"
+source "$(dirname "${BASH_SOURCE[0]}")/src/assert_failure.bash"
+source "$(dirname "${BASH_SOURCE[0]}")/src/assert_output.bash"
+source "$(dirname "${BASH_SOURCE[0]}")/src/refute_output.bash"
+source "$(dirname "${BASH_SOURCE[0]}")/src/assert_line.bash"
+source "$(dirname "${BASH_SOURCE[0]}")/src/refute_line.bash"
diff --git a/src/assert.bash b/src/assert.bash
index efe069a..8f436e5 100644
--- a/src/assert.bash
+++ b/src/assert.bash
@@ -1,30 +1,3 @@
-#
-# bats-assert - Common assertions for Bats
-#
-# Written in 2016 by Zoltan Tombol <zoltan dot tombol at gmail dot com>
-#
-# To the extent possible under law, the author(s) have dedicated all
-# copyright and related and neighboring rights to this software to the
-# public domain worldwide. This software is distributed without any
-# warranty.
-#
-# You should have received a copy of the CC0 Public Domain Dedication
-# along with this software. If not, see
-# <http://creativecommons.org/publicdomain/zero/1.0/>.
-#
-
-#
-# assert.bash
-# -----------
-#
-# Assertions are functions that perform a test and output relevant
-# information on failure to help debugging. They return 1 on failure
-# and 0 otherwise.
-#
-# All output is formatted for readability using the functions of
-# `output.bash' and sent to the standard error.
-#
-
 # Fail and display the expression if it evaluates to false.
 #
 # NOTE: The expression must be a simple command. Compound commands, such
@@ -42,714 +15,7 @@
 assert() {
   if ! "$@"; then
     batslib_print_kv_single 10 'expression' "$*" \
-      | batslib_decorate 'assertion failed' \
-      | fail
-  fi
-}
-
-# Fail and display the expression if it evaluates to true.
-#
-# NOTE: The expression must be a simple command. Compound commands, such
-#       as `[[', can be used only when executed with `bash -c'.
-#
-# Globals:
-#   none
-# Arguments:
-#   $1 - expression
-# Returns:
-#   0 - expression evaluates to FALSE
-#   1 - otherwise
-# Outputs:
-#   STDERR - details, on failure
-refute() {
-  if "$@"; then
-    batslib_print_kv_single 10 'expression' "$*" \
-      | batslib_decorate 'assertion succeeded, but it was expected to fail' \
-      | fail
-  fi
-}
-
-# Fail and display details if the expected and actual values do not
-# equal. Details include both values.
-#
-# Globals:
-#   none
-# Arguments:
-#   $1 - actual value
-#   $2 - expected value
-# Returns:
-#   0 - values equal
-#   1 - otherwise
-# Outputs:
-#   STDERR - details, on failure
-assert_equal() {
-  if [[ $1 != "$2" ]]; then
-    batslib_print_kv_single_or_multi 8 \
-        'expected' "$2" \
-        'actual'   "$1" \
-      | batslib_decorate 'values do not equal' \
-      | fail
-  fi
-}
-
-# Fail and display details if `$status' is not 0. Details include
-# `$status' and `$output'.
-#
-# Globals:
-#   status
-#   output
-# Arguments:
-#   none
-# Returns:
-#   0 - `$status' is 0
-#   1 - otherwise
-# Outputs:
-#   STDERR - details, on failure
-assert_success() {
-  if (( status != 0 )); then
-    { local -ir width=6
-      batslib_print_kv_single "$width" 'status' "$status"
-      batslib_print_kv_single_or_multi "$width" 'output' "$output"
-    } | batslib_decorate 'command failed' \
-      | fail
-  fi
-}
-
-# Fail and display details if `$status' is 0. Details include `$output'.
-#
-# Optionally, when the expected status is specified, fail when it does
-# not equal `$status'. In this case, details include the expected and
-# actual status, and `$output'.
-#
-# Globals:
-#   status
-#   output
-# Arguments:
-#   $1 - [opt] expected status
-# Returns:
-#   0 - `$status' is not 0, or
-#       `$status' equals the expected status
-#   1 - otherwise
-# Outputs:
-#   STDERR - details, on failure
-assert_failure() {
-  (( $# > 0 )) && local -r expected="$1"
-  if (( status == 0 )); then
-    batslib_print_kv_single_or_multi 6 'output' "$output" \
-      | batslib_decorate 'command succeeded, but it was expected to fail' \
-      | fail
-  elif (( $# > 0 )) && (( status != expected )); then
-    { local -ir width=8
-      batslib_print_kv_single "$width" \
-          'expected' "$expected" \
-          'actual'   "$status"
-      batslib_print_kv_single_or_multi "$width" \
-          'output' "$output"
-    } | batslib_decorate 'command failed as expected, but status differs' \
-      | fail
-  fi
-}
-
-# Fail and display details if `$output' does not match the expected
-# output. The expected output can be specified either by the first
-# parameter or on the standard input.
-#
-# By default, literal matching is performed. The assertion fails if the
-# expected output does not equal `$output'. Details include both values.
-#
-# Option `--partial' enables partial matching. The assertion fails if
-# the expected substring cannot be found in `$output'.
-#
-# Option `--regexp' enables regular expression matching. The assertion
-# fails if the extended regular expression does not match `$output'. An
-# invalid regular expression causes an error to be displayed.
-#
-# It is an error to use partial and regular expression matching
-# simultaneously.
-#
-# Globals:
-#   output
-# Options:
-#   -p, --partial - partial matching
-#   -e, --regexp - extended regular expression matching
-#   -, --stdin - read expected output from the standard input
-# Arguments:
-#   $1 - expected output
-# Returns:
-#   0 - expected matches the actual output
-#   1 - otherwise
-# Inputs:
-#   STDIN - [=$1] expected output
-# Outputs:
-#   STDERR - details, on failure
-#            error message, on error
-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 ;;
-      -|--stdin) use_stdin=1; shift ;;
-      --) shift; break ;;
-      *) break ;;
-    esac
-  done
-
-  if (( is_mode_partial )) && (( is_mode_regexp )); then
-    echo "\`--partial' and \`--regexp' are mutually exclusive" \
-      | batslib_decorate 'ERROR: assert_output' \
-      | fail
-    return $?
-  fi
-
-  # Arguments.
-  local expected
-  if (( use_stdin )); then
-    expected="$(cat -)"
-  else
-    expected="$1"
-  fi
-
-  # Matching.
-  if (( is_mode_nonempty )); then
-    if [ -z "$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
-    elif ! [[ $output =~ $expected ]]; then
-      batslib_print_kv_single_or_multi 6 \
-          'regexp'  "$expected" \
-          'output' "$output" \
-        | batslib_decorate 'regular expression does not match output' \
-        | fail
-    fi
-  elif (( is_mode_partial )); then
-    if [[ $output != *"$expected"* ]]; then
-      batslib_print_kv_single_or_multi 9 \
-          'substring' "$expected" \
-          'output'    "$output" \
-        | batslib_decorate 'output does not contain substring' \
-        | fail
-    fi
-  else
-    if [[ $output != "$expected" ]]; then
-      batslib_print_kv_single_or_multi 8 \
-          'expected' "$expected" \
-          'actual'   "$output" \
-        | batslib_decorate 'output differs' \
-        | fail
-    fi
-  fi
-}
-
-# Fail and display details if `$output' matches the unexpected output.
-# The unexpected output can be specified either by the first parameter
-# or on the standard input.
-#
-# By default, literal matching is performed. The assertion fails if the
-# unexpected output equals `$output'. Details include `$output'.
-#
-# Option `--partial' enables partial matching. The assertion fails if
-# the unexpected substring is found in `$output'. The unexpected
-# substring is added to details.
-#
-# Option `--regexp' enables regular expression matching. The assertion
-# fails if the extended regular expression does matches `$output'. The
-# regular expression is added to details. An invalid regular expression
-# causes an error to be displayed.
-#
-# It is an error to use partial and regular expression matching
-# simultaneously.
-#
-# Globals:
-#   output
-# Options:
-#   -p, --partial - partial matching
-#   -e, --regexp - extended regular expression matching
-#   -, --stdin - read unexpected output from the standard input
-# Arguments:
-#   $1 - unexpected output
-# Returns:
-#   0 - unexpected matches the actual output
-#   1 - otherwise
-# Inputs:
-#   STDIN - [=$1] unexpected output
-# Outputs:
-#   STDERR - details, on failure
-#            error message, on error
-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 ;;
-      -|--stdin) use_stdin=1; shift ;;
-      --) shift; break ;;
-      *) break ;;
-    esac
-  done
-
-  if (( is_mode_partial )) && (( is_mode_regexp )); then
-    echo "\`--partial' and \`--regexp' are mutually exclusive" \
-      | batslib_decorate 'ERROR: refute_output' \
-      | fail
-    return $?
-  fi
-
-  # Arguments.
-  local unexpected
-  if (( use_stdin )); then
-    unexpected="$(cat -)"
-  else
-    unexpected="$1"
-  fi
-
-  if (( is_mode_regexp == 1 )) && [[ '' =~ $unexpected ]] || (( $? == 2 )); then
-    echo "Invalid extended regular expression: \`$unexpected'" \
-      | batslib_decorate 'ERROR: refute_output' \
-      | fail
-    return $?
-  fi
-
-  # Matching.
-  if (( is_mode_empty )); then
-    if [ -n "$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" \
-          'output' "$output" \
-        | batslib_decorate 'regular expression should not match output' \
-        | fail
-    fi
-  elif (( is_mode_partial )); then
-    if [[ $output == *"$unexpected"* ]]; then
-      batslib_print_kv_single_or_multi 9 \
-          'substring' "$unexpected" \
-          'output'    "$output" \
-        | batslib_decorate 'output should not contain substring' \
-        | fail
-    fi
-  else
-    if [[ $output == "$unexpected" ]]; then
-      batslib_print_kv_single_or_multi 6 \
-          'output' "$output" \
-        | batslib_decorate 'output equals, but it was expected to differ' \
-        | fail
-    fi
-  fi
-}
-
-# Fail and display details if the expected line is not found in the
-# output (default) or in a specific line of it.
-#
-# By default, the entire output is searched for the expected line. The
-# expected line is matched against every element of `${lines[@]}'. If no
-# match is found, the assertion fails. Details include the expected line
-# and `${lines[@]}'.
-#
-# When `--index <idx>' is specified, only the <idx>-th line is matched.
-# If the expected line does not match `${lines[<idx>]}', the assertion
-# fails. Details include <idx> and the compared lines.
-#
-# By default, literal matching is performed. A literal match fails if
-# the expected string does not equal the matched string.
-#
-# Option `--partial' enables partial matching. A partial match fails if
-# the expected substring is not found in the target string.
-#
-# Option `--regexp' enables regular expression matching. A regular
-# expression match fails if the extended regular expression does not
-# match the target string. An invalid regular expression causes an error
-# to be displayed.
-#
-# It is an error to use partial and regular expression matching
-# simultaneously.
-#
-# Mandatory arguments to long options are mandatory for short options
-# too.
-#
-# Globals:
-#   output
-#   lines
-# Options:
-#   -n, --index <idx> - match the <idx>-th line
-#   -p, --partial - partial matching
-#   -e, --regexp - extended regular expression matching
-# Arguments:
-#   $1 - expected line
-# Returns:
-#   0 - match found
-#   1 - otherwise
-# Outputs:
-#   STDERR - details, on failure
-#            error message, on error
-# FIXME(ztombol): Display `${lines[@]}' instead of `$output'!
-assert_line() {
-  local -i is_match_line=0
-  local -i is_mode_partial=0
-  local -i is_mode_regexp=0
-
-  # Handle options.
-  while (( $# > 0 )); do
-    case "$1" in
-      -n|--index)
-        if (( $# < 2 )) || ! [[ $2 =~ ^([0-9]|[1-9][0-9]+)$ ]]; then
-          echo "\`--index' requires an integer argument: \`$2'" \
-            | batslib_decorate 'ERROR: assert_line' \
-            | fail
-          return $?
-        fi
-        is_match_line=1
-        local -ri idx="$2"
-        shift 2
-        ;;
-      -p|--partial) is_mode_partial=1; shift ;;
-      -e|--regexp) is_mode_regexp=1; shift ;;
-      --) shift; break ;;
-      *) break ;;
-    esac
-  done
-
-  if (( is_mode_partial )) && (( is_mode_regexp )); then
-    echo "\`--partial' and \`--regexp' are mutually exclusive" \
-      | batslib_decorate 'ERROR: assert_line' \
-      | fail
-    return $?
-  fi
-
-  # Arguments.
-  local -r expected="$1"
-
-  if (( is_mode_regexp == 1 )) && [[ '' =~ $expected ]] || (( $? == 2 )); then
-    echo "Invalid extended regular expression: \`$expected'" \
-      | batslib_decorate 'ERROR: assert_line' \
-      | fail
-    return $?
-  fi
-
-  # Matching.
-  if (( is_match_line )); then
-    # Specific line.
-    if (( is_mode_regexp )); then
-      if ! [[ ${lines[$idx]} =~ $expected ]]; then
-        batslib_print_kv_single 6 \
-            'index' "$idx" \
-            'regexp' "$expected" \
-            'line'  "${lines[$idx]}" \
-          | batslib_decorate 'regular expression does not match line' \
-          | fail
-      fi
-    elif (( is_mode_partial )); then
-      if [[ ${lines[$idx]} != *"$expected"* ]]; then
-        batslib_print_kv_single 9 \
-            'index'     "$idx" \
-            'substring' "$expected" \
-            'line'      "${lines[$idx]}" \
-          | batslib_decorate 'line does not contain substring' \
-          | fail
-      fi
-    else
-      if [[ ${lines[$idx]} != "$expected" ]]; then
-        batslib_print_kv_single 8 \
-            'index'    "$idx" \
-            'expected' "$expected" \
-            'actual'   "${lines[$idx]}" \
-          | batslib_decorate 'line differs' \
-          | fail
-      fi
-    fi
-  else
-    # Contained in output.
-    if (( is_mode_regexp )); then
-      local -i idx
-      for (( idx = 0; idx < ${#lines[@]}; ++idx )); do
-        [[ ${lines[$idx]} =~ $expected ]] && return 0
-      done
-      { local -ar single=(
-          'regexp'  "$expected"
-        )
-        local -ar may_be_multi=(
-          'output' "$output"
-        )
-        local -ir width="$( batslib_get_max_single_line_key_width \
-                              "${single[@]}" "${may_be_multi[@]}" )"
-        batslib_print_kv_single "$width" "${single[@]}"
-        batslib_print_kv_single_or_multi "$width" "${may_be_multi[@]}"
-      } | batslib_decorate 'no output line matches regular expression' \
-        | fail
-    elif (( is_mode_partial )); then
-      local -i idx
-      for (( idx = 0; idx < ${#lines[@]}; ++idx )); do
-        [[ ${lines[$idx]} == *"$expected"* ]] && return 0
-      done
-      { local -ar single=(
-          'substring' "$expected"
-        )
-        local -ar may_be_multi=(
-          'output'    "$output"
-        )
-        local -ir width="$( batslib_get_max_single_line_key_width \
-                              "${single[@]}" "${may_be_multi[@]}" )"
-        batslib_print_kv_single "$width" "${single[@]}"
-        batslib_print_kv_single_or_multi "$width" "${may_be_multi[@]}"
-      } | batslib_decorate 'no output line contains substring' \
-        | fail
-    else
-      local -i idx
-      for (( idx = 0; idx < ${#lines[@]}; ++idx )); do
-        [[ ${lines[$idx]} == "$expected" ]] && return 0
-      done
-      { local -ar single=(
-          'line'   "$expected"
-        )
-        local -ar may_be_multi=(
-          'output' "$output"
-        )
-        local -ir width="$( batslib_get_max_single_line_key_width \
-                            "${single[@]}" "${may_be_multi[@]}" )"
-        batslib_print_kv_single "$width" "${single[@]}"
-        batslib_print_kv_single_or_multi "$width" "${may_be_multi[@]}"
-      } | batslib_decorate 'output does not contain line' \
-        | fail
-    fi
-  fi
-}
-
-# Fail and display details if the unexpected line is found in the output
-# (default) or in a specific line of it.
-#
-# By default, the entire output is searched for the unexpected line. The
-# unexpected line is matched against every element of `${lines[@]}'. If
-# a match is found, the assertion fails. Details include the unexpected
-# line, the index of the first match and `${lines[@]}' with the matching
-# line highlighted if `${lines[@]}' is longer than one line.
-#
-# When `--index <idx>' is specified, only the <idx>-th line is matched.
-# If the unexpected line matches `${lines[<idx>]}', the assertion fails.
-# Details include <idx> and the unexpected line.
-#
-# By default, literal matching is performed. A literal match fails if
-# the unexpected string does not equal the matched string.
-#
-# Option `--partial' enables partial matching. A partial match fails if
-# the unexpected substring is found in the target string. When used with
-# `--index <idx>', the unexpected substring is also displayed on
-# failure.
-#
-# Option `--regexp' enables regular expression matching. A regular
-# expression match fails if the extended regular expression matches the
-# target string. When used with `--index <idx>', the regular expression
-# is also displayed on failure. An invalid regular expression causes an
-# error to be displayed.
-#
-# It is an error to use partial and regular expression matching
-# simultaneously.
-#
-# Mandatory arguments to long options are mandatory for short options
-# too.
-#
-# Globals:
-#   output
-#   lines
-# Options:
-#   -n, --index <idx> - match the <idx>-th line
-#   -p, --partial - partial matching
-#   -e, --regexp - extended regular expression matching
-# Arguments:
-#   $1 - unexpected line
-# Returns:
-#   0 - match not found
-#   1 - otherwise
-# Outputs:
-#   STDERR - details, on failure
-#            error message, on error
-# FIXME(ztombol): Display `${lines[@]}' instead of `$output'!
-refute_line() {
-  local -i is_match_line=0
-  local -i is_mode_partial=0
-  local -i is_mode_regexp=0
-
-  # Handle options.
-  while (( $# > 0 )); do
-    case "$1" in
-      -n|--index)
-        if (( $# < 2 )) || ! [[ $2 =~ ^([0-9]|[1-9][0-9]+)$ ]]; then
-          echo "\`--index' requires an integer argument: \`$2'" \
-            | batslib_decorate 'ERROR: refute_line' \
-            | fail
-          return $?
-        fi
-        is_match_line=1
-        local -ri idx="$2"
-        shift 2
-        ;;
-      -p|--partial) is_mode_partial=1; shift ;;
-      -e|--regexp) is_mode_regexp=1; shift ;;
-      --) shift; break ;;
-      *) break ;;
-    esac
-  done
-
-  if (( is_mode_partial )) && (( is_mode_regexp )); then
-    echo "\`--partial' and \`--regexp' are mutually exclusive" \
-      | batslib_decorate 'ERROR: refute_line' \
-      | fail
-    return $?
-  fi
-
-  # Arguments.
-  local -r unexpected="$1"
-
-  if (( is_mode_regexp == 1 )) && [[ '' =~ $unexpected ]] || (( $? == 2 )); then
-    echo "Invalid extended regular expression: \`$unexpected'" \
-      | batslib_decorate 'ERROR: refute_line' \
-      | fail
-    return $?
-  fi
-
-  # Matching.
-  if (( is_match_line )); then
-    # Specific line.
-    if (( is_mode_regexp )); then
-      if [[ ${lines[$idx]} =~ $unexpected ]] || (( $? == 0 )); then
-        batslib_print_kv_single 6 \
-            'index' "$idx" \
-            'regexp' "$unexpected" \
-            'line'  "${lines[$idx]}" \
-          | batslib_decorate 'regular expression should not match line' \
-          | fail
-      fi
-    elif (( is_mode_partial )); then
-      if [[ ${lines[$idx]} == *"$unexpected"* ]]; then
-        batslib_print_kv_single 9 \
-            'index'     "$idx" \
-            'substring' "$unexpected" \
-            'line'      "${lines[$idx]}" \
-          | batslib_decorate 'line should not contain substring' \
-          | fail
-      fi
-    else
-      if [[ ${lines[$idx]} == "$unexpected" ]]; then
-        batslib_print_kv_single 5 \
-            'index' "$idx" \
-            'line'  "${lines[$idx]}" \
-          | batslib_decorate 'line should differ' \
-          | fail
-      fi
-    fi
-  else
-    # Line contained in output.
-    if (( is_mode_regexp )); then
-      local -i idx
-      for (( idx = 0; idx < ${#lines[@]}; ++idx )); do
-        if [[ ${lines[$idx]} =~ $unexpected ]]; then
-          { local -ar single=(
-              'regexp'  "$unexpected"
-              'index'  "$idx"
-            )
-            local -a may_be_multi=(
-              'output' "$output"
-            )
-            local -ir width="$( batslib_get_max_single_line_key_width \
-                                "${single[@]}" "${may_be_multi[@]}" )"
-            batslib_print_kv_single "$width" "${single[@]}"
-            if batslib_is_single_line "${may_be_multi[1]}"; then
-              batslib_print_kv_single "$width" "${may_be_multi[@]}"
-            else
-              may_be_multi[1]="$( printf '%s' "${may_be_multi[1]}" \
-                                    | batslib_prefix \
-                                    | batslib_mark '>' "$idx" )"
-              batslib_print_kv_multi "${may_be_multi[@]}"
-            fi
-          } | batslib_decorate 'no line should match the regular expression' \
-            | fail
-          return $?
-        fi
-      done
-    elif (( is_mode_partial )); then
-      local -i idx
-      for (( idx = 0; idx < ${#lines[@]}; ++idx )); do
-        if [[ ${lines[$idx]} == *"$unexpected"* ]]; then
-          { local -ar single=(
-              'substring' "$unexpected"
-              'index'     "$idx"
-            )
-            local -a may_be_multi=(
-              'output'    "$output"
-            )
-            local -ir width="$( batslib_get_max_single_line_key_width \
-                                "${single[@]}" "${may_be_multi[@]}" )"
-            batslib_print_kv_single "$width" "${single[@]}"
-            if batslib_is_single_line "${may_be_multi[1]}"; then
-              batslib_print_kv_single "$width" "${may_be_multi[@]}"
-            else
-              may_be_multi[1]="$( printf '%s' "${may_be_multi[1]}" \
-                                    | batslib_prefix \
-                                    | batslib_mark '>' "$idx" )"
-              batslib_print_kv_multi "${may_be_multi[@]}"
-            fi
-          } | batslib_decorate 'no line should contain substring' \
-            | fail
-          return $?
-        fi
-      done
-    else
-      local -i idx
-      for (( idx = 0; idx < ${#lines[@]}; ++idx )); do
-        if [[ ${lines[$idx]} == "$unexpected" ]]; then
-          { local -ar single=(
-              'line'   "$unexpected"
-              'index'  "$idx"
-            )
-            local -a may_be_multi=(
-              'output' "$output"
-            )
-            local -ir width="$( batslib_get_max_single_line_key_width \
-                                "${single[@]}" "${may_be_multi[@]}" )"
-            batslib_print_kv_single "$width" "${single[@]}"
-            if batslib_is_single_line "${may_be_multi[1]}"; then
-              batslib_print_kv_single "$width" "${may_be_multi[@]}"
-            else
-              may_be_multi[1]="$( printf '%s' "${may_be_multi[1]}" \
-                                    | batslib_prefix \
-                                    | batslib_mark '>' "$idx" )"
-              batslib_print_kv_multi "${may_be_multi[@]}"
-            fi
-          } | batslib_decorate 'line should not be in output' \
-            | fail
-          return $?
-        fi
-      done
-    fi
+    | batslib_decorate 'assertion failed' \
+    | fail
   fi
 }
diff --git a/src/assert_equal.bash b/src/assert_equal.bash
new file mode 100644
index 0000000..3f0aa80
--- /dev/null
+++ b/src/assert_equal.bash
@@ -0,0 +1,22 @@
+# Fail and display details if the expected and actual values do not
+# equal. Details include both values.
+#
+# Globals:
+#   none
+# Arguments:
+#   $1 - actual value
+#   $2 - expected value
+# Returns:
+#   0 - values equal
+#   1 - otherwise
+# Outputs:
+#   STDERR - details, on failure
+assert_equal() {
+  if [[ $1 != "$2" ]]; then
+    batslib_print_kv_single_or_multi 8 \
+    'expected' "$2" \
+    'actual'   "$1" \
+    | batslib_decorate 'values do not equal' \
+    | fail
+  fi
+}
diff --git a/src/assert_failure.bash b/src/assert_failure.bash
new file mode 100644
index 0000000..1a797f4
--- /dev/null
+++ b/src/assert_failure.bash
@@ -0,0 +1,35 @@
+# Fail and display details if `$status' is 0. Details include `$output'.
+#
+# Optionally, when the expected status is specified, fail when it does
+# not equal `$status'. In this case, details include the expected and
+# actual status, and `$output'.
+#
+# Globals:
+#   status
+#   output
+# Arguments:
+#   $1 - [opt] expected status
+# Returns:
+#   0 - `$status' is not 0, or
+#       `$status' equals the expected status
+#   1 - otherwise
+# Outputs:
+#   STDERR - details, on failure
+assert_failure() {
+  (( $# > 0 )) && local -r expected="$1"
+  if (( status == 0 )); then
+    batslib_print_kv_single_or_multi 6 'output' "$output" \
+    | batslib_decorate 'command succeeded, but it was expected to fail' \
+    | fail
+  elif (( $# > 0 )) && (( status != expected )); then
+    { local -ir width=8
+      batslib_print_kv_single "$width" \
+      'expected' "$expected" \
+      'actual'   "$status"
+      batslib_print_kv_single_or_multi "$width" \
+      'output' "$output"
+    } \
+    | batslib_decorate 'command failed as expected, but status differs' \
+    | fail
+  fi
+}
diff --git a/src/assert_line.bash b/src/assert_line.bash
new file mode 100644
index 0000000..2ab427a
--- /dev/null
+++ b/src/assert_line.bash
@@ -0,0 +1,163 @@
+# Fail and display details if the expected line is not found in the
+# output (default) or in a specific line of it.
+#
+# By default, the entire output is searched for the expected line. The
+# expected line is matched against every element of `${lines[@]}'. If no
+# match is found, the assertion fails. Details include the expected line
+# and `${lines[@]}'.
+#
+# When `--index <idx>' is specified, only the <idx>-th line is matched.
+# If the expected line does not match `${lines[<idx>]}', the assertion
+# fails. Details include <idx> and the compared lines.
+#
+# By default, literal matching is performed. A literal match fails if
+# the expected string does not equal the matched string.
+#
+# Option `--partial' enables partial matching. A partial match fails if
+# the expected substring is not found in the target string.
+#
+# Option `--regexp' enables regular expression matching. A regular
+# expression match fails if the extended regular expression does not
+# match the target string. An invalid regular expression causes an error
+# to be displayed.
+#
+# It is an error to use partial and regular expression matching
+# simultaneously.
+#
+# Mandatory arguments to long options are mandatory for short options
+# too.
+#
+# Globals:
+#   output
+#   lines
+# Options:
+#   -n, --index <idx> - match the <idx>-th line
+#   -p, --partial - partial matching
+#   -e, --regexp - extended regular expression matching
+# Arguments:
+#   $1 - expected line
+# Returns:
+#   0 - match found
+#   1 - otherwise
+# Outputs:
+#   STDERR - details, on failure
+#            error message, on error
+# FIXME(ztombol): Display `${lines[@]}' instead of `$output'!
+assert_line() {
+  local -i is_match_line=0
+  local -i is_mode_partial=0
+  local -i is_mode_regexp=0
+
+  # Handle options.
+  while (( $# > 0 )); do
+    case "$1" in
+    -n|--index)
+      if (( $# < 2 )) || ! [[ $2 =~ ^([0-9]|[1-9][0-9]+)$ ]]; then
+        echo "\`--index' requires an integer argument: \`$2'" \
+        | batslib_decorate 'ERROR: assert_line' \
+        | fail
+        return $?
+      fi
+      is_match_line=1
+      local -ri idx="$2"
+      shift 2
+      ;;
+    -p|--partial) is_mode_partial=1; shift ;;
+    -e|--regexp) is_mode_regexp=1; shift ;;
+    --) shift; break ;;
+    *) break ;;
+    esac
+  done
+
+  if (( is_mode_partial )) && (( is_mode_regexp )); then
+    echo "\`--partial' and \`--regexp' are mutually exclusive" \
+    | batslib_decorate 'ERROR: assert_line' \
+    | fail
+    return $?
+  fi
+
+  # Arguments.
+  local -r expected="$1"
+
+  if (( is_mode_regexp == 1 )) && [[ '' =~ $expected ]] || (( $? == 2 )); then
+    echo "Invalid extended regular expression: \`$expected'" \
+    | batslib_decorate 'ERROR: assert_line' \
+    | fail
+    return $?
+  fi
+
+  # Matching.
+  if (( is_match_line )); then
+    # Specific line.
+    if (( is_mode_regexp )); then
+      if ! [[ ${lines[$idx]} =~ $expected ]]; then
+        batslib_print_kv_single 6 \
+        'index' "$idx" \
+        'regexp' "$expected" \
+        'line'  "${lines[$idx]}" \
+        | batslib_decorate 'regular expression does not match line' \
+        | fail
+      fi
+    elif (( is_mode_partial )); then
+      if [[ ${lines[$idx]} != *"$expected"* ]]; then
+        batslib_print_kv_single 9 \
+        'index'     "$idx" \
+        'substring' "$expected" \
+        'line'      "${lines[$idx]}" \
+        | batslib_decorate 'line does not contain substring' \
+        | fail
+      fi
+    else
+      if [[ ${lines[$idx]} != "$expected" ]]; then
+        batslib_print_kv_single 8 \
+        'index'    "$idx" \
+        'expected' "$expected" \
+        'actual'   "${lines[$idx]}" \
+        | batslib_decorate 'line differs' \
+        | fail
+      fi
+    fi
+  else
+    # Contained in output.
+    if (( is_mode_regexp )); then
+      local -i idx
+      for (( idx = 0; idx < ${#lines[@]}; ++idx )); do
+        [[ ${lines[$idx]} =~ $expected ]] && return 0
+      done
+      { local -ar single=( 'regexp' "$expected" )
+        local -ar may_be_multi=( 'output' "$output" )
+        local -ir width="$( batslib_get_max_single_line_key_width "${single[@]}" "${may_be_multi[@]}" )"
+        batslib_print_kv_single "$width" "${single[@]}"
+        batslib_print_kv_single_or_multi "$width" "${may_be_multi[@]}"
+      } \
+      | batslib_decorate 'no output line matches regular expression' \
+      | fail
+    elif (( is_mode_partial )); then
+      local -i idx
+      for (( idx = 0; idx < ${#lines[@]}; ++idx )); do
+        [[ ${lines[$idx]} == *"$expected"* ]] && return 0
+      done
+      { local -ar single=( 'substring' "$expected" )
+        local -ar may_be_multi=( 'output' "$output" )
+        local -ir width="$( batslib_get_max_single_line_key_width "${single[@]}" "${may_be_multi[@]}" )"
+        batslib_print_kv_single "$width" "${single[@]}"
+        batslib_print_kv_single_or_multi "$width" "${may_be_multi[@]}"
+      } \
+      | batslib_decorate 'no output line contains substring' \
+      | fail
+    else
+      local -i idx
+      for (( idx = 0; idx < ${#lines[@]}; ++idx )); do
+        [[ ${lines[$idx]} == "$expected" ]] && return 0
+      done
+      { local -ar single=( 'line' "$expected" )
+        local -ar may_be_multi=( 'output' "$output" )
+        local -ir width="$( batslib_get_max_single_line_key_width "${single[@]}" "${may_be_multi[@]}" )"
+        batslib_print_kv_single "$width" "${single[@]}"
+        batslib_print_kv_single_or_multi "$width" "${may_be_multi[@]}"
+      } \
+      | batslib_decorate 'output does not contain line' \
+      | fail
+    fi
+  fi
+}
diff --git a/src/assert_output.bash b/src/assert_output.bash
new file mode 100644
index 0000000..ec10547
--- /dev/null
+++ b/src/assert_output.bash
@@ -0,0 +1,106 @@
+# Fail and display details if `$output' does not match the expected
+# output. The expected output can be specified either by the first
+# parameter or on the standard input.
+#
+# By default, literal matching is performed. The assertion fails if the
+# expected output does not equal `$output'. Details include both values.
+#
+# Option `--partial' enables partial matching. The assertion fails if
+# the expected substring cannot be found in `$output'.
+#
+# Option `--regexp' enables regular expression matching. The assertion
+# fails if the extended regular expression does not match `$output'. An
+# invalid regular expression causes an error to be displayed.
+#
+# It is an error to use partial and regular expression matching
+# simultaneously.
+#
+# Globals:
+#   output
+# Options:
+#   -p, --partial - partial matching
+#   -e, --regexp - extended regular expression matching
+#   -, --stdin - read expected output from the standard input
+# Arguments:
+#   $1 - expected output
+# Returns:
+#   0 - expected matches the actual output
+#   1 - otherwise
+# Inputs:
+#   STDIN - [=$1] expected output
+# Outputs:
+#   STDERR - details, on failure
+#            error message, on error
+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 ;;
+    -|--stdin) use_stdin=1; shift ;;
+    --) shift; break ;;
+    *) break ;;
+    esac
+  done
+
+  if (( is_mode_partial )) && (( is_mode_regexp )); then
+    echo "\`--partial' and \`--regexp' are mutually exclusive" \
+    | batslib_decorate 'ERROR: assert_output' \
+    | fail
+    return $?
+  fi
+
+  # Arguments.
+  local expected
+  if (( use_stdin )); then
+    expected="$(cat -)"
+  else
+    expected="$1"
+  fi
+
+  # Matching.
+  if (( is_mode_nonempty )); then
+    if [ -z "$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
+    elif ! [[ $output =~ $expected ]]; then
+      batslib_print_kv_single_or_multi 6 \
+      'regexp'  "$expected" \
+      'output' "$output" \
+      | batslib_decorate 'regular expression does not match output' \
+      | fail
+    fi
+  elif (( is_mode_partial )); then
+    if [[ $output != *"$expected"* ]]; then
+      batslib_print_kv_single_or_multi 9 \
+      'substring' "$expected" \
+      'output'    "$output" \
+      | batslib_decorate 'output does not contain substring' \
+      | fail
+    fi
+  else
+    if [[ $output != "$expected" ]]; then
+      batslib_print_kv_single_or_multi 8 \
+      'expected' "$expected" \
+      'actual'   "$output" \
+      | batslib_decorate 'output differs' \
+      | fail
+    fi
+  fi
+}
diff --git a/src/assert_success.bash b/src/assert_success.bash
new file mode 100644
index 0000000..e7d285b
--- /dev/null
+++ b/src/assert_success.bash
@@ -0,0 +1,23 @@
+# Fail and display details if `$status' is not 0. Details include
+# `$status' and `$output'.
+#
+# Globals:
+#   status
+#   output
+# Arguments:
+#   none
+# Returns:
+#   0 - `$status' is 0
+#   1 - otherwise
+# Outputs:
+#   STDERR - details, on failure
+assert_success() {
+  if (( status != 0 )); then
+    { local -ir width=6
+      batslib_print_kv_single "$width" 'status' "$status"
+      batslib_print_kv_single_or_multi "$width" 'output' "$output"
+    } \
+    | batslib_decorate 'command failed' \
+    | fail
+  fi
+}
diff --git a/src/refute.bash b/src/refute.bash
new file mode 100644
index 0000000..61c8197
--- /dev/null
+++ b/src/refute.bash
@@ -0,0 +1,21 @@
+# Fail and display the expression if it evaluates to true.
+#
+# NOTE: The expression must be a simple command. Compound commands, such
+#       as `[[', can be used only when executed with `bash -c'.
+#
+# Globals:
+#   none
+# Arguments:
+#   $1 - expression
+# Returns:
+#   0 - expression evaluates to FALSE
+#   1 - otherwise
+# Outputs:
+#   STDERR - details, on failure
+refute() {
+  if "$@"; then
+    batslib_print_kv_single 10 'expression' "$*" \
+    | batslib_decorate 'assertion succeeded, but it was expected to fail' \
+    | fail
+  fi
+}
diff --git a/src/refute_line.bash b/src/refute_line.bash
new file mode 100644
index 0000000..332c384
--- /dev/null
+++ b/src/refute_line.bash
@@ -0,0 +1,187 @@
+# Fail and display details if the unexpected line is found in the output
+# (default) or in a specific line of it.
+#
+# By default, the entire output is searched for the unexpected line. The
+# unexpected line is matched against every element of `${lines[@]}'. If
+# a match is found, the assertion fails. Details include the unexpected
+# line, the index of the first match and `${lines[@]}' with the matching
+# line highlighted if `${lines[@]}' is longer than one line.
+#
+# When `--index <idx>' is specified, only the <idx>-th line is matched.
+# If the unexpected line matches `${lines[<idx>]}', the assertion fails.
+# Details include <idx> and the unexpected line.
+#
+# By default, literal matching is performed. A literal match fails if
+# the unexpected string does not equal the matched string.
+#
+# Option `--partial' enables partial matching. A partial match fails if
+# the unexpected substring is found in the target string. When used with
+# `--index <idx>', the unexpected substring is also displayed on
+# failure.
+#
+# Option `--regexp' enables regular expression matching. A regular
+# expression match fails if the extended regular expression matches the
+# target string. When used with `--index <idx>', the regular expression
+# is also displayed on failure. An invalid regular expression causes an
+# error to be displayed.
+#
+# It is an error to use partial and regular expression matching
+# simultaneously.
+#
+# Mandatory arguments to long options are mandatory for short options
+# too.
+#
+# Globals:
+#   output
+#   lines
+# Options:
+#   -n, --index <idx> - match the <idx>-th line
+#   -p, --partial - partial matching
+#   -e, --regexp - extended regular expression matching
+# Arguments:
+#   $1 - unexpected line
+# Returns:
+#   0 - match not found
+#   1 - otherwise
+# Outputs:
+#   STDERR - details, on failure
+#            error message, on error
+# FIXME(ztombol): Display `${lines[@]}' instead of `$output'!
+refute_line() {
+  local -i is_match_line=0
+  local -i is_mode_partial=0
+  local -i is_mode_regexp=0
+
+  # Handle options.
+  while (( $# > 0 )); do
+    case "$1" in
+    -n|--index)
+      if (( $# < 2 )) || ! [[ $2 =~ ^([0-9]|[1-9][0-9]+)$ ]]; then
+        echo "\`--index' requires an integer argument: \`$2'" \
+        | batslib_decorate 'ERROR: refute_line' \
+        | fail
+        return $?
+      fi
+      is_match_line=1
+      local -ri idx="$2"
+      shift 2
+      ;;
+    -p|--partial) is_mode_partial=1; shift ;;
+    -e|--regexp) is_mode_regexp=1; shift ;;
+    --) shift; break ;;
+    *) break ;;
+    esac
+  done
+
+  if (( is_mode_partial )) && (( is_mode_regexp )); then
+    echo "\`--partial' and \`--regexp' are mutually exclusive" \
+    | batslib_decorate 'ERROR: refute_line' \
+    | fail
+    return $?
+  fi
+
+  # Arguments.
+  local -r unexpected="$1"
+
+  if (( is_mode_regexp == 1 )) && [[ '' =~ $unexpected ]] || (( $? == 2 )); then
+    echo "Invalid extended regular expression: \`$unexpected'" \
+    | batslib_decorate 'ERROR: refute_line' \
+    | fail
+    return $?
+  fi
+
+  # Matching.
+  if (( is_match_line )); then
+    # Specific line.
+    if (( is_mode_regexp )); then
+      if [[ ${lines[$idx]} =~ $unexpected ]] || (( $? == 0 )); then
+        batslib_print_kv_single 6 \
+        'index' "$idx" \
+        'regexp' "$unexpected" \
+        'line'  "${lines[$idx]}" \
+        | batslib_decorate 'regular expression should not match line' \
+        | fail
+      fi
+    elif (( is_mode_partial )); then
+      if [[ ${lines[$idx]} == *"$unexpected"* ]]; then
+        batslib_print_kv_single 9 \
+        'index'     "$idx" \
+        'substring' "$unexpected" \
+        'line'      "${lines[$idx]}" \
+        | batslib_decorate 'line should not contain substring' \
+        | fail
+      fi
+    else
+      if [[ ${lines[$idx]} == "$unexpected" ]]; then
+        batslib_print_kv_single 5 \
+        'index' "$idx" \
+        'line'  "${lines[$idx]}" \
+        | batslib_decorate 'line should differ' \
+        | fail
+      fi
+    fi
+  else
+    # Line contained in output.
+    if (( is_mode_regexp )); then
+      local -i idx
+      for (( idx = 0; idx < ${#lines[@]}; ++idx )); do
+        if [[ ${lines[$idx]} =~ $unexpected ]]; then
+          { local -ar single=( 'regexp' "$unexpected" 'index' "$idx" )
+            local -a may_be_multi=( 'output' "$output" )
+            local -ir width="$( batslib_get_max_single_line_key_width "${single[@]}" "${may_be_multi[@]}" )"
+            batslib_print_kv_single "$width" "${single[@]}"
+            if batslib_is_single_line "${may_be_multi[1]}"; then
+              batslib_print_kv_single "$width" "${may_be_multi[@]}"
+            else
+              may_be_multi[1]="$( printf '%s' "${may_be_multi[1]}" | batslib_prefix | batslib_mark '>' "$idx" )"
+              batslib_print_kv_multi "${may_be_multi[@]}"
+            fi
+          } \
+          | batslib_decorate 'no line should match the regular expression' \
+          | fail
+          return $?
+        fi
+      done
+    elif (( is_mode_partial )); then
+      local -i idx
+      for (( idx = 0; idx < ${#lines[@]}; ++idx )); do
+        if [[ ${lines[$idx]} == *"$unexpected"* ]]; then
+          { local -ar single=( 'substring' "$unexpected" 'index' "$idx" )
+            local -a may_be_multi=( 'output' "$output" )
+            local -ir width="$( batslib_get_max_single_line_key_width "${single[@]}" "${may_be_multi[@]}" )"
+            batslib_print_kv_single "$width" "${single[@]}"
+            if batslib_is_single_line "${may_be_multi[1]}"; then
+              batslib_print_kv_single "$width" "${may_be_multi[@]}"
+            else
+              may_be_multi[1]="$( printf '%s' "${may_be_multi[1]}" | batslib_prefix | batslib_mark '>' "$idx" )"
+              batslib_print_kv_multi "${may_be_multi[@]}"
+            fi
+          } \
+          | batslib_decorate 'no line should contain substring' \
+          | fail
+          return $?
+        fi
+      done
+    else
+      local -i idx
+      for (( idx = 0; idx < ${#lines[@]}; ++idx )); do
+        if [[ ${lines[$idx]} == "$unexpected" ]]; then
+          { local -ar single=( 'line' "$unexpected" 'index' "$idx" )
+            local -a may_be_multi=( 'output' "$output" )
+            local -ir width="$( batslib_get_max_single_line_key_width "${single[@]}" "${may_be_multi[@]}" )"
+            batslib_print_kv_single "$width" "${single[@]}"
+            if batslib_is_single_line "${may_be_multi[1]}"; then
+              batslib_print_kv_single "$width" "${may_be_multi[@]}"
+            else
+              may_be_multi[1]="$( printf '%s' "${may_be_multi[1]}" | batslib_prefix | batslib_mark '>' "$idx" )"
+              batslib_print_kv_multi "${may_be_multi[@]}"
+            fi
+          } \
+          | batslib_decorate 'line should not be in output' \
+          | fail
+          return $?
+        fi
+      done
+    fi
+  fi
+}
diff --git a/src/refute_output.bash b/src/refute_output.bash
new file mode 100644
index 0000000..93298f6
--- /dev/null
+++ b/src/refute_output.bash
@@ -0,0 +1,111 @@
+# Fail and display details if `$output' matches the unexpected output.
+# The unexpected output can be specified either by the first parameter
+# or on the standard input.
+#
+# By default, literal matching is performed. The assertion fails if the
+# unexpected output equals `$output'. Details include `$output'.
+#
+# Option `--partial' enables partial matching. The assertion fails if
+# the unexpected substring is found in `$output'. The unexpected
+# substring is added to details.
+#
+# Option `--regexp' enables regular expression matching. The assertion
+# fails if the extended regular expression does matches `$output'. The
+# regular expression is added to details. An invalid regular expression
+# causes an error to be displayed.
+#
+# It is an error to use partial and regular expression matching
+# simultaneously.
+#
+# Globals:
+#   output
+# Options:
+#   -p, --partial - partial matching
+#   -e, --regexp - extended regular expression matching
+#   -, --stdin - read unexpected output from the standard input
+# Arguments:
+#   $1 - unexpected output
+# Returns:
+#   0 - unexpected matches the actual output
+#   1 - otherwise
+# Inputs:
+#   STDIN - [=$1] unexpected output
+# Outputs:
+#   STDERR - details, on failure
+#            error message, on error
+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 ;;
+    -|--stdin) use_stdin=1; shift ;;
+    --) shift; break ;;
+    *) break ;;
+    esac
+  done
+
+  if (( is_mode_partial )) && (( is_mode_regexp )); then
+    echo "\`--partial' and \`--regexp' are mutually exclusive" \
+    | batslib_decorate 'ERROR: refute_output' \
+    | fail
+    return $?
+  fi
+
+  # Arguments.
+  local unexpected
+  if (( use_stdin )); then
+    unexpected="$(cat -)"
+  else
+    unexpected="$1"
+  fi
+
+  if (( is_mode_regexp == 1 )) && [[ '' =~ $unexpected ]] || (( $? == 2 )); then
+    echo "Invalid extended regular expression: \`$unexpected'" \
+    | batslib_decorate 'ERROR: refute_output' \
+    | fail
+    return $?
+  fi
+
+  # Matching.
+  if (( is_mode_empty )); then
+    if [ -n "$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" \
+      'output' "$output" \
+      | batslib_decorate 'regular expression should not match output' \
+      | fail
+    fi
+  elif (( is_mode_partial )); then
+    if [[ $output == *"$unexpected"* ]]; then
+      batslib_print_kv_single_or_multi 9 \
+      'substring' "$unexpected" \
+      'output'    "$output" \
+      | batslib_decorate 'output should not contain substring' \
+      | fail
+    fi
+  else
+    if [[ $output == "$unexpected" ]]; then
+      batslib_print_kv_single_or_multi 6 \
+      'output' "$output" \
+      | batslib_decorate 'output equals, but it was expected to differ' \
+      | fail
+    fi
+  fi
+}