Bug#41893: main.variables mysql-test fails if new variable like '%alloc%' is added.

Started fix in 5.0 as the same issue is here.
Revising queries used given what appears to be the scope of this test to only select the manipulated variables.
Added tests for values that are / are not multiples of 1024 to test rounding / constraints.
This behavior is not currently documented (docs bug has been opened)

mysql-test/r/variables.result

@@ -236,32 +236,66 @@ set @@rand_seed1=10000000,@@rand_seed2=1000000;
 select ROUND(RAND(),5);
 ROUND(RAND(),5)
 0.02887
-show variables like '%alloc%';
+
+==+ Testing %alloc% system variables +==
+==+ NOTE:  These values *must* be a multiple of 1024 +==
+==+ Other values will be rounded down to nearest multiple +==
+
+==+ Show initial values +==
+SHOW VARIABLES WHERE variable_name IN ('range_alloc_block_size',
+'query_alloc_block_size', 'query_prealloc_size',
+'transaction_alloc_block_size', 'transaction_prealloc_size');
 Variable_name	Value
 query_alloc_block_size	8192
 query_prealloc_size	8192
 range_alloc_block_size	4096
 transaction_alloc_block_size	8192
 transaction_prealloc_size	4096
-set @@range_alloc_block_size=1024*16;
+==+ Manipulate variable values +=
+Testing values that are multiples of 1024
+set @@range_alloc_block_size=1024*15+1024;
+set @@query_alloc_block_size=1024*15+1024*2;
+set @@query_prealloc_size=1024*18-1024;
+set @@transaction_alloc_block_size=1024*21-1024*1;
+set @@transaction_prealloc_size=1024*21-2048;
+==+ Check manipulated values ==+
+SHOW VARIABLES WHERE variable_name IN ('range_alloc_block_size',
+'query_alloc_block_size', 'query_prealloc_size',
+'transaction_alloc_block_size', 'transaction_prealloc_size');
+Variable_name	Value
+query_alloc_block_size	17408
+query_prealloc_size	17408
+range_alloc_block_size	16384
+transaction_alloc_block_size	20480
+transaction_prealloc_size	19456
+==+ Manipulate variable values +==
+Testing values that are not 1024 multiples
+set @@range_alloc_block_size=1024*16+1023;
 set @@query_alloc_block_size=1024*17+2;
-set @@query_prealloc_size=1024*18;
+set @@query_prealloc_size=1024*18-1023;
 set @@transaction_alloc_block_size=1024*20-1;
 set @@transaction_prealloc_size=1024*21-1;
 select @@query_alloc_block_size;
 @@query_alloc_block_size
 17408
-show variables like '%alloc%';
+==+ Check manipulated values ==+
+SHOW VARIABLES WHERE variable_name IN ('range_alloc_block_size',
+'query_alloc_block_size', 'query_prealloc_size',
+'transaction_alloc_block_size', 'transaction_prealloc_size');
 Variable_name	Value
 query_alloc_block_size	17408
-query_prealloc_size	18432
+query_prealloc_size	17408
 range_alloc_block_size	16384
 transaction_alloc_block_size	19456
 transaction_prealloc_size	20480
+==+ Set values back to the default values +==
 set @@range_alloc_block_size=default;
 set @@query_alloc_block_size=default, @@query_prealloc_size=default;
 set transaction_alloc_block_size=default, @@transaction_prealloc_size=default;
-show variables like '%alloc%';
+==+ Check the values not that they are reset +==
+SHOW VARIABLES WHERE variable_name IN ('range_alloc_block_size',
+'query_alloc_block_size', 'query_prealloc_size',
+'transaction_alloc_block_size', 'transaction_prealloc_size');
 Variable_name	Value
 query_alloc_block_size	8192
 query_prealloc_size	8192

mysql-test/t/variables.test

@@ -150,18 +150,46 @@ select @@timestamp>0;
 set @@rand_seed1=10000000,@@rand_seed2=1000000;
 select ROUND(RAND(),5);
 
-show variables like '%alloc%';
-set @@range_alloc_block_size=1024*16;
+--echo
+--echo ==+ Testing %alloc% system variables +==
+--echo ==+ NOTE:  These values *must* be a multiple of 1024 +==
+--echo ==+ Other values will be rounded down to nearest multiple +==
+--echo
+--echo ==+ Show initial values +==
+SHOW VARIABLES WHERE variable_name IN ('range_alloc_block_size',
+'query_alloc_block_size', 'query_prealloc_size',
+'transaction_alloc_block_size', 'transaction_prealloc_size');
+--echo ==+ Manipulate variable values +=
+--echo Testing values that are multiples of 1024
+set @@range_alloc_block_size=1024*15+1024;
+set @@query_alloc_block_size=1024*15+1024*2;
+set @@query_prealloc_size=1024*18-1024;
+set @@transaction_alloc_block_size=1024*21-1024*1;
+set @@transaction_prealloc_size=1024*21-2048;
+--echo ==+ Check manipulated values ==+
+SHOW VARIABLES WHERE variable_name IN ('range_alloc_block_size',
+'query_alloc_block_size', 'query_prealloc_size',
+'transaction_alloc_block_size', 'transaction_prealloc_size');
+--echo ==+ Manipulate variable values +==
+--echo Testing values that are not 1024 multiples
+set @@range_alloc_block_size=1024*16+1023;
 set @@query_alloc_block_size=1024*17+2;
-set @@query_prealloc_size=1024*18;
+set @@query_prealloc_size=1024*18-1023;
 set @@transaction_alloc_block_size=1024*20-1;
 set @@transaction_prealloc_size=1024*21-1;
 select @@query_alloc_block_size;
-show variables like '%alloc%';
+--echo ==+ Check manipulated values ==+
+SHOW VARIABLES WHERE variable_name IN ('range_alloc_block_size',
+'query_alloc_block_size', 'query_prealloc_size',
+'transaction_alloc_block_size', 'transaction_prealloc_size');
+--echo ==+ Set values back to the default values +==
 set @@range_alloc_block_size=default;
 set @@query_alloc_block_size=default, @@query_prealloc_size=default;
 set transaction_alloc_block_size=default, @@transaction_prealloc_size=default;
-show variables like '%alloc%';
+--echo ==+ Check the values not that they are reset +==
+SHOW VARIABLES WHERE variable_name IN ('range_alloc_block_size',
+'query_alloc_block_size', 'query_prealloc_size',
+'transaction_alloc_block_size', 'transaction_prealloc_size');
 
 #
 # Bug #10904 Illegal mix of collations between