5.41Salesforce automation can surprise you

A Mule upsert may cause:

validation rules
flows
triggers
workflow
duplicate rules
other automation

which might:

reject record
change additional fields
create related records
send events

Therefore, when testing integration:

request
  ↓
Mule
  ↓
Salesforce write

don't necessarily verify only the fields Mule sent.

You may need to validate the resulting Salesforce state.