diff --git a/tests/network/test-lib-self-test.sh b/tests/network/test-lib-self-test.sh
new file mode 100755
index 00000000..917e7b33
--- /dev/null
+++ b/tests/network/test-lib-self-test.sh
@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+# Regression checks for test assertions: matching error output must not pass.
+set -euo pipefail
+cd "$(dirname "$0")"
+source ./test-lib.sh
+
+LOG_DIR=$(mktemp -d)
+trap 'test_cleanup; rm -rf "$LOG_DIR"' EXIT
+CURRENT_LOG="$LOG_DIR/assertions.log"
+: > "$CURRENT_LOG"
+
+assert_output_contains "printf 'ready\\n'" ready "successful output matches"
+if assert_output_contains "printf 'ready\\n'; exit 7" ready "failed command must not match"; then
+    echo 'assert_output_contains accepted a failed command' >&2
+    exit 1
+fi
+if assert_output_contains "printf 'not-ready\\n'" '^ready$' "missing pattern must not match"; then
+    echo 'assert_output_contains accepted a missing pattern' >&2
+    exit 1
+fi
+[ "$TESTS_RUN" -eq 3 ] && [ "$TESTS_PASSED" -eq 1 ] && [ "$TESTS_FAILED" -eq 2 ]
+echo 'network assertion self-test passed'
diff --git a/tests/network/test-lib.sh b/tests/network/test-lib.sh
index b513c2c3..e2e829e1 100755
--- a/tests/network/test-lib.sh
+++ b/tests/network/test-lib.sh
@@ -188,10 +188,12 @@ assert_output_contains() {
     echo "  Expected pattern: $pattern" >> "$CURRENT_LOG"
     
     local output
-    output=$(eval "$cmd" 2>&1)
+    local command_status=0
+    output=$(eval "$cmd" 2>&1) || command_status=$?
+    echo "  Exit status: $command_status" >> "$CURRENT_LOG"
     echo "  Output: $output" >> "$CURRENT_LOG"
-    
-    if echo "$output" | grep -q "$pattern"; then
+
+    if [ "$command_status" -eq 0 ] && grep -q "$pattern" <<< "$output"; then
         TESTS_PASSED=$((TESTS_PASSED + 1))
         echo -e "  ${GREEN}✓${NC} $msg"
         echo "  Result: PASS" >> "$CURRENT_LOG"
@@ -199,7 +201,7 @@ assert_output_contains() {
     else
         TESTS_FAILED=$((TESTS_FAILED + 1))
         echo -e "  ${RED}✗${NC} $msg"
-        echo "  Result: FAIL (pattern not found)" >> "$CURRENT_LOG"
+        echo "  Result: FAIL (exit status $command_status or pattern not found)" >> "$CURRENT_LOG"
         return 1
     fi
 }