Add tests for '-f' option in dropdb utility.

This will test that the force option works when there is an active backend
connected to the database being dropped.

Author: Pavel Stehule and Vignesh C
Reviewed-by: Amit Kapila and Vignesh C
Discussion: https://postgr.es/m/CAP_rwwmLJJbn70vLOZFpxGw3XD7nLB_7+NKz46H5EOO2k5H7OQ@mail.gmail.com

src/bin/scripts/t/050_dropdb.pl

@@ -3,7 +3,7 @@ use warnings;
 
 use PostgresNode;
 use TestLib;
-use Test::More tests => 13;
+use Test::More tests => 11;
 
 program_help_ok('dropdb');
 program_version_ok('dropdb');
@@ -19,11 +19,5 @@ $node->issues_sql_like(
 	qr/statement: DROP DATABASE foobar1/,
 	'SQL DROP DATABASE run');
 
-$node->safe_psql('postgres', 'CREATE DATABASE foobar2');
-$node->issues_sql_like(
-	[ 'dropdb', '--force', 'foobar2' ],
-	qr/statement: DROP DATABASE foobar2 WITH \(FORCE\);/,
-	'SQL DROP DATABASE (FORCE) run');
-
 $node->command_fails([ 'dropdb', 'nonexistent' ],
 	'fails with nonexistent database');

src/bin/scripts/t/051_dropdb_force.pl

@@ -0,0 +1,104 @@
+#
+# Tests the force option of drop database command.
+#
+use strict;
+use warnings;
+
+use PostgresNode;
+use TestLib;
+use Test::More tests => 9;
+
+# To avoid hanging while expecting some specific input from a psql
+# instance being driven by us, add a timeout high enough that it
+# should never trigger even on very slow machines, unless something
+# is really wrong.
+my $psql_timeout = IPC::Run::timer(60);
+
+my $node = get_new_node('master');
+$node->init;
+$node->start;
+
+# Create a database that will be dropped.  This will test that the force
+# option works when no other backend is connected to the database being
+# dropped.
+$node->safe_psql('postgres', 'CREATE DATABASE foobar');
+$node->issues_sql_like(
+        [ 'dropdb', '--force', 'foobar' ],
+        qr/statement: DROP DATABASE foobar WITH \(FORCE\);/,
+        'SQL DROP DATABASE (FORCE) run');
+
+# database foobar must not exist.
+is( $node->safe_psql(
+		'postgres',
+		qq[SELECT EXISTS(SELECT * FROM pg_database WHERE datname='foobar');]
+	),
+	'f',
+	'database foobar was removed');
+
+# Create a database that will be dropped.  This will test that the force
+# option works when one other backend is connected to the database being
+# dropped.
+$node->safe_psql('postgres', 'CREATE DATABASE foobar1');
+
+# Run psql, keeping session alive, so we have an alive backend to kill.
+my ($killme_stdin, $killme_stdout, $killme_stderr) = ('', '', '');
+my $killme = IPC::Run::start(
+	[
+		'psql', '-X', '-qAt', '-v', 'ON_ERROR_STOP=1', '-f', '-', '-d',
+		$node->connstr('foobar1')
+	],
+	'<',
+	\$killme_stdin,
+	'>',
+	\$killme_stdout,
+	'2>',
+	\$killme_stderr,
+	$psql_timeout);
+
+# Ensure killme process is active.
+$killme_stdin .= q[
+SELECT pg_backend_pid();
+];
+ok( TestLib::pump_until(
+		$killme, $psql_timeout, \$killme_stdout, qr/[[:digit:]]+[\r\n]$/m),
+	'acquired pid for SIGTERM');
+my $pid = $killme_stdout;
+chomp($pid);
+$killme_stdout = '';
+$killme_stderr = '';
+
+# Check the connections on foobar1 database.
+is( $node->safe_psql(
+		'postgres',
+		qq[SELECT pid FROM pg_stat_activity WHERE datname='foobar1' AND pid = $pid;]
+	),
+	$pid,
+	'database foobar1 is used');
+
+# Now drop database with dropdb --force command.
+$node->issues_sql_like(
+	[ 'dropdb', '--force', 'foobar1' ],
+	qr/statement: DROP DATABASE foobar1 WITH \(FORCE\);/,
+	'SQL DROP DATABASE (FORCE) run');
+
+# Check that psql sees the killed backend as having been terminated.
+$killme_stdin .= q[
+SELECT 1;
+];
+ok( TestLib::pump_until(
+		$killme, $psql_timeout, \$killme_stderr,
+		qr/FATAL:  terminating connection due to administrator command/m),
+	"psql query died successfully after SIGTERM");
+$killme_stderr = '';
+$killme_stdout = '';
+$killme->finish;
+
+# database foobar1 must not exist.
+is( $node->safe_psql(
+		'postgres',
+		qq[SELECT EXISTS(SELECT * FROM pg_database WHERE datname='foobar1');]
+	),
+	'f',
+	'database foobar1 was removed');
+
+$node->stop();