Bug #38360: BLACKHOLE replication with RBR is broken

Incremental patch to add comments to test cases.

mysql-test/extra/rpl_tests/rpl_blackhole.test

+# Check replication of one statement assuming that the engine on the
+# slave is a blackhole engine.
+
+# Input:
+# $statement    Statement to evaluate, it is assumed to change t1
+
+# 1. Evaluate statement on master, it is assumed to change t1
+# 2. Wait for statement to be processed on slave
+# 3. SELECT from table t1 to see what was written
+# 4. Compare position on slave before executing statement and after
+#    executing statement. If difference is >0, then something was
+#    written to the binary log on the slave.
+
 connection slave;
 let $before = query_get_value("SHOW MASTER STATUS", Position, 1);
 

mysql-test/suite/rpl/t/rpl_blackhole.test

 --source include/master-slave.inc
 
-# Test to test that blackhole works with replication, all three
-# modes. We start by creating a table on the master and then change
+# PURPOSE. Test that blackhole works with replication in all three
+# modes: STATEMENT, MIXED, and ROW.
+#
+# METHOD. We start by creating a table on the master and then change
 # the engine to use blackhole on the slave.
+#
+# After insert/update/delete of one or more rows, the test the
+# proceeds to check that replication is running after replicating an
+# change, that the blackhole engine does not contain anything (which
+# is just a check that the correct engine is used), and that something
+# is written to the binary log.
+#
+# Whe check INSERT, UPDATE, and DELETE statement for tables with no
+# key (forcing a range search on the slave), primary keys (using a
+# primary key lookup), and index/key with multiple matches (forcing an
+# index search).
 
 # We start with no primary key
 CREATE TABLE t1 (a INT, b INT, c INT);