test_bitmapset: Improve random function

test_random_operations() did not check the result returned by
bms_is_member() in its last phase, when checking that the contents of
the bitmap match with what is expected.  This was impacting the
reliability of the function and the coverage it could provide.

This commit improves the whole function, adding more checks based on
bms_is_member(), using a bitmap and a secondary array that tracks the
members added by random additions and deletions.

While on it, more comments are added to document the internals of the
function.

Reported-by: Ranier Vilela <ranier.vf@gmail.com>
Author: Greg Burd <greg@burd.me>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: David Rowley <dgrowleyml@gmail.com>
Discussion: https://postgr.es/m/CAEudQAq_zOSA2NUQSWePTGV_=90Uw0WcXxGOWnN-vwF046OOqA@mail.gmail.com

1 files changed, 44 insertions, 13 deletions

diff --git a/src/test/modules/test_bitmapset/test_bitmapset.c b/src/test/modules/test_bitmapset/test_bitmapset.c
index 8bc9b1f48e9..8162285fcb3 100644
--- a/src/test/modules/test_bitmapset/test_bitmapset.c
+++ b/src/test/modules/test_bitmapset/test_bitmapset.c
@@ -616,25 +616,31 @@ test_random_operations(PG_FUNCTION_ARGS)
 	min_value = PG_GETARG_INT32(3);
 
 	pg_prng_seed(&state, seed);
+
+	/*
+	 * There can be up to "num_ops" members added.  This is very unlikely,
+	 * still possible if all the operations hit the "0" case during phase 4
+	 * where multiple operation types are mixed together.
+	 */
 	members = palloc(sizeof(int) * num_ops);
 
-	/* Phase 1: Random insertions */
+	/* Phase 1: Random insertions in first set */
 	for (int i = 0; i < num_ops / 2; i++)
 	{
 		member = pg_prng_uint32(&state) % max_range + min_value;
 
 		if (!bms_is_member(member, bms1))
-		{
 			members[num_members++] = member;
-			bms1 = bms_add_member(bms1, member);
-		}
+		bms1 = bms_add_member(bms1, member);
 	}
 
-	/* Phase 2: Random set operations */
+	/* Phase 2: Random insertions in second set */
 	for (int i = 0; i < num_ops / 4; i++)
 	{
 		member = pg_prng_uint32(&state) % max_range + min_value;
 
+		if (!bms_is_member(member, bms2))
+			members[num_members++] = member;
 		bms2 = bms_add_member(bms2, member);
 	}
 
@@ -642,7 +648,7 @@ test_random_operations(PG_FUNCTION_ARGS)
 	result = bms_union(bms1, bms2);
 	EXPECT_NOT_NULL(result);
 
-	/* Verify union contains all members from first set */
+	/* Verify union contains all members from first and second sets */
 	for (int i = 0; i < num_members; i++)
 	{
 		if (!bms_is_member(members[i], result))
@@ -650,7 +656,10 @@ test_random_operations(PG_FUNCTION_ARGS)
 	}
 	bms_free(result);
 
-	/* Test intersection */
+	/*
+	 * Test intersection, checking that all the members in the result are from
+	 * both the first and second sets.
+	 */
 	result = bms_intersect(bms1, bms2);
 	if (result != NULL)
 	{
@@ -679,28 +688,49 @@ test_random_operations(PG_FUNCTION_ARGS)
 		bms_free(result);
 	}
 
-	pfree(members);
 	bms_free(bms1);
 	bms_free(bms2);
 
-	for (int i = 0; i < num_ops; i++)
+	/*
+	 * Phase 4: mix of operations on a single set, cross-checking a bitmap
+	 * with a secondary state, "members".
+	 */
+	num_members = 0;
+
+	for (int op = 0; op < num_ops; op++)
 	{
-		member = pg_prng_uint32(&state) % max_range + min_value;
 		switch (pg_prng_uint32(&state) % 3)
 		{
 			case 0:				/* add */
+				member = pg_prng_uint32(&state) % max_range + min_value;
+				if (!bms_is_member(member, bms))
+					members[num_members++] = member;
 				bms = bms_add_member(bms, member);
 				break;
 			case 1:				/* delete */
-				if (bms != NULL)
+				if (num_members > 0)
 				{
+					int			pos = pg_prng_uint32(&state) % num_members;
+
+					member = members[pos];
+					if (!bms_is_member(member, bms))
+						elog(ERROR, "expected %d to be a valid member", member);
+
 					bms = bms_del_member(bms, member);
+
+					/*
+					 * Move the final array member at the position of the
+					 * member just deleted, reducing the array size by one.
+					 */
+					members[pos] = members[--num_members];
 				}
 				break;
 			case 2:				/* test membership */
-				if (bms != NULL)
+				/* Verify that bitmap contains all members */
+				for (int i = 0; i < num_members; i++)
 				{
-					bms_is_member(member, bms);
+					if (!bms_is_member(members[i], bms))
+						elog(ERROR, "missing member %d", members[i]);
 				}
 				break;
 		}
@@ -708,6 +738,7 @@ test_random_operations(PG_FUNCTION_ARGS)
 	}
 
 	bms_free(bms);
+	pfree(members);
 
 	PG_RETURN_INT32(total_ops);
 }