feat: Print stderr in assert_success/failure

src/assert_failure.bash

@@ -61,7 +61,12 @@ assert_failure() {
 
   (( $# > 0 )) && local -r expected="$1"
   if (( status == 0 )); then
-    batslib_print_kv_single_or_multi 6 'output' "$output" \
+    { local -ir width=6
+      batslib_print_kv_single_or_multi "$width" 'output' "$output"
+      if [[ -n "$stderr" ]]; then
+        batslib_print_kv_single_or_multi "$width" 'stderr' "$stderr"
+      fi
+    } \
     | batslib_decorate 'command succeeded, but it was expected to fail' \
     | fail
   elif (( $# > 0 )) && (( status != expected )); then
@@ -71,6 +76,9 @@ assert_failure() {
       'actual'   "$status"
       batslib_print_kv_single_or_multi "$width" \
       'output' "$output"
+      if [[ -n "$stderr" ]]; then
+      	batslib_print_kv_single_or_multi "$width" 'stderr' "$stderr"
+      fi
     } \
     | batslib_decorate 'command failed as expected, but status differs' \
     | fail

src/assert_success.bash

@@ -37,6 +37,9 @@ assert_success() {
     { local -ir width=6
       batslib_print_kv_single "$width" 'status' "$status"
       batslib_print_kv_single_or_multi "$width" 'output' "$output"
+      if [[ -n "$stderr" ]]; then
+      	batslib_print_kv_single_or_multi "$width" 'stderr' "$stderr"
+      fi
     } \
     | batslib_decorate 'command failed' \
     | fail

test/assert_failure.bats

@@ -21,6 +21,24 @@ output : a
 ERR_MSG
 }
 
+@test "assert_failure(): returns 1 and displays \`\$stderr' if it is set" {
+	run --separate-stderr \
+			bash -c 'echo "a"
+							 echo "b" >&2
+							 exit 0'
+	run assert_failure
+
+	echo "Stderr: $stderr" >&3
+
+	assert_test_fail <<'ERR_MSG'
+
+-- command succeeded, but it was expected to fail --
+output : a
+stderr : b
+--
+ERR_MSG
+}
+
 @test "assert_failure(): displays \`\$output' in multi-line format if it is longer then one line" {
   run bash -c 'printf "a 0\na 1"
                exit 0'
@@ -73,3 +91,4 @@ output (2 lines):
 --
 ERR_MSG
 }
+

test/assert_success.bats

@@ -38,3 +38,20 @@ output (2 lines):
 --
 ERR_MSG
 }
+
+@test "assert_success(): displays \`\$stderr' if it is set" {
+	run --separate-stderr \
+			bash -c 'echo "a"
+							 echo "b" >&2
+							 exit 1'
+	run assert_success
+
+	assert_test_fail <<'ERR_MSG'
+
+-- command failed --
+status : 1
+output : a
+stderr : b
+--
+ERR_MSG
+}