diff --git a/xCAT-test/unit/probe_utils_tcp_listener.t b/xCAT-test/unit/probe_utils_tcp_listener.t
new file mode 100644
index 000000000..2fae8a973
--- /dev/null
+++ b/xCAT-test/unit/probe_utils_tcp_listener.t
@@ -0,0 +1,114 @@
+#!/usr/bin/env perl
+use strict;
+use warnings;
+
+use FindBin;
+use lib "$FindBin::Bin/../../xCAT-probe/lib/perl";
+
+use Test::More;
+
+require probe_utils;
+
+my $ss_output = <<'EOF';
+State  Recv-Q Send-Q Local Address:Port Peer Address:Port Process
+LISTEN 0      128          0.0.0.0:3001      0.0.0.0:*
+LISTEN 0      128             [::]:3002         [::]:* users:(("xcatd",pid=100,fd=5))
+LISTEN 0      511                *:80               *:* users:(("httpd",pid=200,fd=4))
+EOF
+
+my $netstat_output = <<'EOF';
+Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
+tcp        0      0 0.0.0.0:3001            0.0.0.0:*               LISTEN      100/xcatd
+tcp6       0      0 :::3002                 :::*                    LISTEN      100/xcatd
+tcp6       0      0 :::80                   :::*                    LISTEN      200/apache2
+EOF
+
+ok(probe_utils::_tcp_listener_output_has_port($ss_output, 3001), 'ss IPv4 listener is detected');
+ok(probe_utils::_tcp_listener_output_has_port($ss_output, 3002), 'ss IPv6 listener is detected');
+ok(!probe_utils::_tcp_listener_output_has_port($ss_output, 300), 'ss listener requires an exact port match');
+ok(probe_utils::_tcp_listener_output_has_port($ss_output, 80, qr/httpd|apache/), 'ss listener process can be matched');
+ok(!probe_utils::_tcp_listener_output_has_port($ss_output, 80, qr/xcatd/), 'ss listener rejects the wrong process');
+
+ok(probe_utils::_tcp_listener_output_has_port($netstat_output, 3001), 'netstat IPv4 listener is detected');
+ok(probe_utils::_tcp_listener_output_has_port($netstat_output, 3002), 'netstat IPv6 listener is detected');
+ok(probe_utils::_tcp_listener_output_has_port($netstat_output, 80, qr/httpd|apache/), 'netstat listener process can be matched');
+ok(!probe_utils::_tcp_listener_output_has_port($netstat_output, 0), 'invalid port is rejected');
+ok(!probe_utils::_tcp_listener_output_has_port($netstat_output, 'http'), 'non-numeric port is rejected');
+
+{
+    no warnings 'redefine';
+    my @commands;
+    local *probe_utils::_command_available = sub { return 1; };
+    local *probe_utils::_capture_command_output = sub {
+        push @commands, [@_];
+        return $ss_output;
+    };
+
+    ok(probe_utils->is_tcp_port_listening(3001), 'class-style listener check succeeds with ss');
+    is_deeply($commands[0], ['ss', '-lnt'], 'listener check prefers ss');
+}
+
+{
+    no warnings 'redefine';
+    my @commands;
+    local *probe_utils::_command_available = sub { return 1; };
+    local *probe_utils::_capture_command_output = sub {
+        push @commands, [@_];
+        return $ss_output;
+    };
+
+    ok(probe_utils::is_tcp_port_listening(80, qr/httpd|apache/), 'process-aware listener check succeeds with ss');
+    is_deeply($commands[0], ['ss', '-lntp'], 'process-aware listener check requests ss process data');
+}
+
+{
+    no warnings 'redefine';
+    my @commands;
+    local *probe_utils::_command_available = sub { return 1; };
+    local *probe_utils::_capture_command_output = sub {
+        push @commands, [@_];
+        return $_[0] eq 'ss' ? $ss_output : $netstat_output;
+    };
+
+    ok(!probe_utils::is_tcp_port_listening(4000), 'successful ss output is authoritative when a port is absent');
+    is(scalar(@commands), 1, 'missing port in successful ss output does not consult netstat');
+}
+
+{
+    no warnings 'redefine';
+    my @commands;
+    local *probe_utils::_command_available = sub { return 1; };
+    local *probe_utils::_capture_command_output = sub {
+        push @commands, [@_];
+        return if $_[0] eq 'ss';
+        return $netstat_output;
+    };
+
+    ok(probe_utils::is_tcp_port_listening(3002), 'listener check falls back when ss fails');
+    is_deeply(
+        \@commands,
+        [['ss', '-lnt'], ['netstat', '-ant']],
+        'failed ss invocation falls back to netstat'
+    );
+}
+
+{
+    no warnings 'redefine';
+    my @commands;
+    local *probe_utils::_command_available = sub { return $_[0] eq 'netstat'; };
+    local *probe_utils::_capture_command_output = sub {
+        push @commands, [@_];
+        return $netstat_output;
+    };
+
+    ok(probe_utils::is_tcp_port_listening(80, qr/httpd|apache/), 'process-aware listener check uses netstat fallback');
+    is_deeply($commands[0], ['netstat', '-tnlp'], 'process-aware fallback preserves legacy netstat options');
+}
+
+{
+    no warnings 'redefine';
+    local *probe_utils::_command_available = sub { return 0; };
+    ok(!probe_utils::is_tcp_port_listening(3001), 'missing socket inspection commands fail cleanly');
+}
+
+done_testing();