Add a simple test for contrib/auto_explain.

This module formerly had zero test coverage.

Discussion: https://postgr.es/m/1445881.1611441692@sss.pgh.pa.us

contrib/auto_explain/.gitignore

+# Generated subdirectories
+/log/
+/results/
+/tmp_check/

contrib/auto_explain/Makefile

@@ -6,6 +6,8 @@ OBJS = \
 	auto_explain.o
 PGFILEDESC = "auto_explain - logging facility for execution plans"
 
+TAP_TESTS = 1
+
 ifdef USE_PGXS
 PG_CONFIG = pg_config
 PGXS := $(shell $(PG_CONFIG) --pgxs)

contrib/auto_explain/t/001_auto_explain.pl

+use strict;
+use warnings;
+
+use PostgresNode;
+use TestLib;
+use Test::More tests => 4;
+
+my $node = get_new_node('main');
+$node->init;
+$node->append_conf('postgresql.conf',
+	"shared_preload_libraries = 'auto_explain'");
+$node->append_conf('postgresql.conf', "auto_explain.log_min_duration = 0");
+$node->append_conf('postgresql.conf', "auto_explain.log_analyze = on");
+$node->start;
+
+# run a couple of queries
+$node->safe_psql("postgres", "SELECT * FROM pg_class;");
+$node->safe_psql("postgres",
+	"SELECT * FROM pg_proc WHERE proname = 'int4pl';");
+
+# emit some json too
+$node->append_conf('postgresql.conf', "auto_explain.log_format = json");
+$node->reload;
+$node->safe_psql("postgres", "SELECT * FROM pg_proc;");
+$node->safe_psql("postgres",
+	"SELECT * FROM pg_class WHERE relname = 'pg_class';");
+
+$node->stop('fast');
+
+my $log = $node->logfile();
+
+my $log_contents = slurp_file($log);
+
+like(
+	$log_contents,
+	qr/Seq Scan on pg_class/,
+	"sequential scan logged, text mode");
+
+like(
+	$log_contents,
+	qr/Index Scan using pg_proc_proname_args_nsp_index on pg_proc/,
+	"index scan logged, text mode");
+
+like(
+	$log_contents,
+	qr/"Node Type": "Seq Scan"[^}]*"Relation Name": "pg_proc"/s,
+	"sequential scan logged, json mode");
+
+like(
+	$log_contents,
+	qr/"Node Type": "Index Scan"[^}]*"Index Name": "pg_class_relname_nsp_index"/s,
+	"index scan logged, json mode");