how to identify the transactions that are causing the transaction log to grow?
Try this extended event (change the filename path accordingly).  I've used it in the past to help me track down what was causing unexpected growth in my data and log files.

CREATE EVENT SESSION [DB Size Tracking] ON SERVER 
ADD EVENT sqlserver.database_file_size_change(
    ACTION(sqlserver.client_app_name,sqlserver.client_hostname,sqlserver.database_name,sqlserver.nt_username,sqlserver.plan_handle,sqlserver.query_hash,sqlserver.query_plan_hash,sqlserver.server_principal_name,sqlserver.session_id,sqlserver.session_nt_username,sqlserver.sql_text,sqlserver.username))
ADD TARGET package0.event_file(SET filename=N'E:\ExtendedEvent\DB Size Tracking.xel')
WITH (MAX_MEMORY=4096 KB,EVENT_RETENTION_MODE=ALLOW_SINGLE_EVENT_LOSS,MAX_DISPATCH_LATENCY=30 SECONDS,MAX_EVENT_SIZE=0 KB,MEMORY_PARTITION_MODE=NONE,TRACK_CAUSALITY=OFF,STARTUP_STATE=ON)
GO


You'll need to shrink your log on the TEST server, then let the jobs run so that it grows again.  This extended event will then log the SQL text of what causes the autogrowth event.