Steps to reproduce:
Precondition: server is running, host was previously created

1. On the existing host, click Create item
2. Use Item configuration:

   Name: test
   Type: Script
   Key: test
   Parameter: test , Value: {{HOST.NAME}.btoa()}
   Script: return 0;
   

3. Click test
4. See the resolved macro in the Item test pop-up

Note: any macro function with or without parameters can be used, and will return same result.

Result:
Empty value is displayed in the form. Error in the log:

Undefined array key "{{HOST.NAME}.btoa()}" [zabbix.php:17 -> require_once() -> ZBase->run() -> ZBase->processRequest() -> CController->run() -> CControllerPopupItemTestEdit->doAction() -> CMacrosResolverHelper::extractItemTestMacros() -> CMacrosResolver::extractItemTestMacros() -> CConfigFile->{closure}() in include/classes/macros/CMacrosResolver.php:1664] 

See video:
:

Expected:
Macro function should be correctly resolved in the item test form.