diff --git a/tests/libtest.sh b/tests/libtest.sh
index 572f023c..afdf3649 100755
--- a/tests/libtest.sh
+++ b/tests/libtest.sh
@@ -100,13 +100,17 @@ assert_has_dir () {
 
 assert_not_has_file () {
     if test -f "$1"; then
-	echo 1>&2 "File '$1' exists"; exit 1
+        sed -e 's/^/# /' < "$1" >&2
+        echo 1>&2 "File '$1' exists"
+        exit 1
     fi
 }
 
 assert_not_file_has_content () {
     if grep -q -e "$2" "$1"; then
-	echo 1>&2 "File '$1' incorrectly matches regexp '$2'"; exit 1
+        sed -e 's/^/# /' < "$1" >&2
+        echo 1>&2 "File '$1' incorrectly matches regexp '$2'"
+        exit 1
     fi
 }
 
@@ -118,13 +122,17 @@ assert_not_has_dir () {
 
 assert_file_has_content () {
     if ! grep -q -e "$2" "$1"; then
-	echo 1>&2 "File '$1' doesn't match regexp '$2'"; exit 1
+        sed -e 's/^/# /' < "$1" >&2
+        echo 1>&2 "File '$1' doesn't match regexp '$2'"
+        exit 1
     fi
 }
 
 assert_file_empty() {
     if test -s "$1"; then
-	echo 1>&2 "File '$1' is not empty"; exit 1
+        sed -e 's/^/# /' < "$1" >&2
+        echo 1>&2 "File '$1' is not empty"
+        exit 1
     fi
 }