Add a test harness for the red-black tree code.

This improves the regression tests' coverage of rbtree.c from pretty
awful (because some of the functions aren't used yet) to basically 100%.

Victor Drobny, reviewed by Aleksander Alekseev and myself

Discussion: https://postgr.es/m/c9d61310e16e75f8acaf6cb1c48b7b77@postgrespro.ru

src/test/modules/Makefile

@@ -13,6 +13,7 @@ SUBDIRS = \
 		  test_extensions \
 		  test_parser \
 		  test_pg_dump \
+		  test_rbtree \
 		  test_rls_hooks \
 		  test_shm_mq \
 		  worker_spi

src/test/modules/test_rbtree/.gitignore

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

src/test/modules/test_rbtree/Makefile

+# src/test/modules/test_rbtree/Makefile
+
+MODULE_big = test_rbtree
+OBJS = test_rbtree.o $(WIN32RES)
+PGFILEDESC = "test_rbtree - test code for red-black tree library"
+
+EXTENSION = test_rbtree
+DATA = test_rbtree--1.0.sql
+
+REGRESS = test_rbtree
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = src/test/modules/test_rbtree
+top_builddir = ../../../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif

src/test/modules/test_rbtree/README

+test_rbtree is a test module for checking the correctness of red-black
+tree operations.
+
+These tests are performed on red-black trees that store integers.
+Since the rbtree logic treats the comparison function as a black
+box, it shouldn't be important exactly what the key type is.
+
+Checking the correctness of traversals is based on the fact that a red-black
+tree is a binary search tree, so the elements should be visited in increasing
+(for Left-Current-Right) or decreasing (for Right-Current-Left) order.
+
+Also, this module does some checks of the correctness of the find, delete
+and leftmost operations.

src/test/modules/test_rbtree/expected/test_rbtree.out

+CREATE EXTENSION test_rbtree;
+--
+-- These tests don't produce any interesting output.  We're checking that
+-- the operations complete without crashing or hanging and that none of their
+-- internal sanity tests fail.
+--
+SELECT test_rb_tree(10000);
+ test_rb_tree 
+--------------
+ 
+(1 row)
+

src/test/modules/test_rbtree/sql/test_rbtree.sql

+CREATE EXTENSION test_rbtree;
+
+--
+-- These tests don't produce any interesting output.  We're checking that
+-- the operations complete without crashing or hanging and that none of their
+-- internal sanity tests fail.
+--
+SELECT test_rb_tree(10000);

src/test/modules/test_rbtree/test_rbtree--1.0.sql

+/* src/test/modules/test_rbtree/test_rbtree--1.0.sql */
+
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION test_rbtree" to load this file. \quit
+
+CREATE FUNCTION test_rb_tree(size INTEGER)
+	RETURNS pg_catalog.void STRICT
+	AS 'MODULE_PATHNAME' LANGUAGE C;

src/test/modules/test_rbtree/test_rbtree.control

+comment = 'Test code for red-black tree library'
+default_version = '1.0'
+module_pathname = '$libdir/test_rbtree'
+relocatable = true