From dbd78ae258dbb09550b300b6b5453d536d3656ee Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Mon, 6 Oct 2025 18:41:30 -0400
Subject: [PATCH v6 3/3] Add a TAP test to exercise psql's use of the pager.

Up to now, we have had zero test coverage of these code paths,
because they aren't reached unless isatty(stdout).  We do have
the test infrastructure to improve that situation, though.
Following the lead of 010_tab_completion.pl, set up an
interactive psql and feed it some test cases.

To detect whether it really did invoke the pager, point
PSQL_PAGER to "wc -l".  The test is skipped if that utility
isn't available.

Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/2dd2430f-dd20-4c89-97fd-242616a3d768@ewie.name
---
 src/bin/psql/meson.build    |   1 +
 src/bin/psql/t/030_pager.pl | 104 ++++++++++++++++++++++++++++++++++++
 2 files changed, 105 insertions(+)
 create mode 100644 src/bin/psql/t/030_pager.pl

diff --git a/src/bin/psql/meson.build b/src/bin/psql/meson.build
index f795ff28271..d344053c23b 100644
--- a/src/bin/psql/meson.build
+++ b/src/bin/psql/meson.build
@@ -77,6 +77,7 @@ tests += {
       't/001_basic.pl',
       't/010_tab_completion.pl',
       't/020_cancel.pl',
+      't/030_pager.pl',
     ],
   },
 }
diff --git a/src/bin/psql/t/030_pager.pl b/src/bin/psql/t/030_pager.pl
new file mode 100644
index 00000000000..dd2be340e55
--- /dev/null
+++ b/src/bin/psql/t/030_pager.pl
@@ -0,0 +1,104 @@
+
+# Copyright (c) 2021-2025, PostgreSQL Global Development Group
+
+use strict;
+use warnings FATAL => 'all';
+
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+use Data::Dumper;
+
+# If we don't have IO::Pty, forget it, because IPC::Run depends on that
+# to support pty connections
+eval { require IO::Pty; };
+if ($@)
+{
+	plan skip_all => 'IO::Pty is needed to run this test';
+}
+
+# Check that "wc -l" does what we expect, else forget it
+my $wcstdin = "foo bar\nbaz\n";
+my ($wcstdout, $wcstderr);
+my $result = IPC::Run::run [ 'wc', '-l' ],
+  '<' => \$wcstdin,
+  '>' => \$wcstdout,
+  '2>' => \$wcstderr;
+chomp $wcstdout;
+if ($wcstdout ne '2' || $wcstderr ne '')
+{
+	plan skip_all => '"wc -l" is needed to run this test';
+}
+
+# We set up "wc -l" as the pager so we can tell whether psql used the pager
+$ENV{PSQL_PAGER} = "wc -l";
+
+# start a new server
+my $node = PostgreSQL::Test::Cluster->new('main');
+$node->init;
+$node->start;
+
+# fire up an interactive psql session
+my $h = $node->interactive_psql('postgres');
+
+# set the pty's window size to known values
+# (requires undesirable chumminess with the innards of IPC::Run)
+for my $pty (values %{ $h->{run}->{PTYS} })
+{
+	$pty->set_winsize(24, 80);
+}
+
+# Simple test case: type something and see if psql responds as expected
+sub do_command
+{
+	my ($send, $pattern, $annotation) = @_;
+
+	# report test failures from caller location
+	local $Test::Builder::Level = $Test::Builder::Level + 1;
+
+	# restart per-command timer
+	$h->{timeout}->start($PostgreSQL::Test::Utils::timeout_default);
+
+	# send the data to be sent and wait for its result
+	my $out = $h->query_until($pattern, $send);
+	my $okay = ($out =~ $pattern && !$h->{timeout}->is_expired);
+	ok($okay, $annotation);
+	# for debugging, log actual output if it didn't match
+	local $Data::Dumper::Terse = 1;
+	local $Data::Dumper::Useqq = 1;
+	diag 'Actual output was ' . Dumper($out) . "Did not match \"$pattern\"\n"
+	  if !$okay;
+	return;
+}
+
+# Test invocation of the pager
+#
+# Note that interactive_psql starts psql with --no-align --tuples-only,
+# and that the output string will include psql's prompts and command echo.
+
+do_command(
+	"SELECT 'test' AS t FROM generate_series(1,23);\n",
+	qr/^test\r?$/m,
+	"execute SELECT query that needs no pagination");
+
+do_command(
+	"SELECT 'test' AS t FROM generate_series(1,24);\n",
+	qr/^24\r?$/m,
+	"execute SELECT query that needs pagination");
+
+do_command(
+	"\\pset expanded\nSELECT generate_series(1,20) as g;\n",
+	qr/^39\r?$/m,
+	"execute SELECT query that needs pagination in expanded mode");
+
+do_command(
+	"\\pset tuples_only off\n\\d+ information_schema.referential_constraints\n",
+	qr/^\d+\r?$/m,
+	"execute command with footer that needs pagination");
+
+# send psql an explicit \q to shut it down, else pty won't close properly
+$h->quit or die "psql returned $?";
+
+# done
+$node->stop;
+done_testing();
-- 
2.43.7