Hi,
 
Agreed with everything except one place:
  
>> diff --git a/test/box/gh-3290-ddl_collation_deleted.test.lua b/test/box/gh-3290-ddl_collation_deleted.test.lua
>> new file mode 100644
>> index 000000000..f36838e7a
>> --- /dev/null
>> +++ b/test/box/gh-3290-ddl_collation_deleted.test.lua
>> @@ -0,0 +1,10 @@
>> +env = require('test_run')
>> +test_run = env.new()
>
>unused variables
>
>> +--
>> +-- gh-3290: expose ICU into Lua. It uses built-in collations, that
>> +-- must work even if a collation is deleted from _collation.
>> +--
>> +t = box.space._collation:delete{1}
>> +utf8.cmp('abc', 'def')
>> +box.space._collation:replace(t)
>
>missed cleanup
> 
In this place cleanup not needed.
The last line restores the original state or «cleanup»
 
>--
>sergeyb@ 
 
 
--
Oleg Piskunov