Improve pg_amcheck's TAP test 003_check.pl.

Disable autovacuum, because we don't want it to run against
intentionally corrupted tables. Also, before corrupting the tables,
run pg_amcheck and ensure that it passes. Otherwise, if something
unexpected happens when we check the corrupted tables, it's not so
clear whether it would have also happened before we corrupted
them.

Mark Dilger

Discussion: http://postgr.es/m/AA5506CE-7D2A-42E4-A51D-358635E3722D@enterprisedb.com

src/bin/pg_amcheck/t/003_check.pl

@@ -3,7 +3,7 @@ use warnings;
 
 use PostgresNode;
 use TestLib;
-use Test::More tests => 60;
+use Test::More tests => 63;
 
 my ($node, $port, %corrupt_page, %remove_relation);
 
@@ -117,6 +117,7 @@ sub perform_all_corruptions()
 # Test set-up
 $node = get_new_node('test');
 $node->init;
+$node->append_conf('postgresql.conf', 'autovacuum=off');
 $node->start;
 $port = $node->port;
 
@@ -308,11 +309,6 @@ plan_to_remove_relation_file('db2', 's1.t1_btree');
 # Leave 'db3' uncorrupted
 #
 
-# Perform the corruptions we planned above using only a single database restart.
-#
-perform_all_corruptions();
-
-
 # Standard first arguments to TestLib functions
 my @cmd = ('pg_amcheck', '--quiet', '-p', $port);
 
@@ -322,6 +318,22 @@ my $line_pointer_corruption_re = qr/line pointer/;
 my $missing_file_re = qr/could not open file ".*": No such file or directory/;
 my $index_missing_relation_fork_re = qr/index ".*" lacks a main relation fork/;
 
+# We have created test databases with tables populated with data, but have not
+# yet corrupted anything.  As such, we expect no corruption and verify that
+# none is reported
+#
+$node->command_checks_all(
+	[ @cmd, '-d', 'db1', '-d', 'db2', '-d', 'db3' ],
+	0,
+	[ $no_output_re ],
+	[ $no_output_re ],
+	'pg_amcheck prior to corruption');
+
+# Perform the corruptions we planned above using only a single database restart.
+#
+perform_all_corruptions();
+
+
 # Checking databases with amcheck installed and corrupt relations, pg_amcheck
 # command itself should return exit status = 2, because tables and indexes are
 # corrupt, not exit status = 1, which would mean the pg_amcheck command itself