Check availability of module injection_points in TAP tests

This fixes defects with installcheck for TAP tests that expect the
module injection_points to exist in an installation, but the contents of
src/test/modules are not installed by default with installcheck.  This
would cause, for example, failures under installcheck-world for a build
with injection points enabled, when the contents of src/test/modules/
are not installed.

The availability of the module can be done with a scan of
pg_available_extension.  This has been introduced in 2cdcae9da696, and
it is refactored here as a new routine in Cluster.pm.

Tests are changed in different ways depending on what they need:
- The libpq TAP test sets up a node even without injection points, so it
is enough to check that CREATE EXTENSION can be used.  There is no need
for the variable enable_injection_points.
- In test_misc, 006_signal_autovacuum requires a runtime check.
- 041_checkpoint_at_promote in recovery tests and 005_timeouts in
test_misc are updated to use the routine introduced in Cluster.pm.
- test_slru's 001_multixact, injection_points's 001_stats and
modules/gin/ do not require a check as these modules disable
installcheck entirely.

Discussion: https://postgr.es/m/ZtesYQ-WupeAK7xK@paquier.xyz

1 files changed, 22 insertions, 0 deletions

diff --git a/src/test/perl/PostgreSQL/Test/Cluster.pm b/src/test/perl/PostgreSQL/Test/Cluster.pm
index fe6ebf10f76..143dc8c1015 100644
--- a/src/test/perl/PostgreSQL/Test/Cluster.pm
+++ b/src/test/perl/PostgreSQL/Test/Cluster.pm
@@ -2837,6 +2837,28 @@ sub lsn
 
 =pod
 
+=item $node->check_extension(extension_name)
+
+Scan pg_available_extensions to check that an extension is available in an
+installation.
+
+Returns 1 if the extension is available, 0 otherwise.
+
+=cut
+
+sub check_extension
+{
+	my ($self, $extension_name) = @_;
+
+	my $result = $self->safe_psql('postgres',
+		"SELECT count(*) > 0 FROM pg_available_extensions WHERE name = '$extension_name';"
+	);
+
+	return $result eq 't' ? 1 : 0;
+}
+
+=pod
+
 =item $node->wait_for_event(wait_event_name, backend_type)
 
 Poll pg_stat_activity until backend_type reaches wait_event_name.