Not a question, but my experiences, from which hopefully someone may learn something.
Salesforce has announced that workflows and processes must eventually be replaced by flows.
Our org has 4 workflows related to OpportunityLineItem that do all kinds of processing with Quantity and UnitPrice. I have created a single before-creation/update flow that captures all functionality of the workflows. I have tested this by first creating Apex unit tests that cover the behavior of the workflows.
Afterwards, I disabled the workflows, enabled the flow and reran the unit tests. Creating unit tests for OpportunityLineItem objects is tricky, by the way, because Quantity, Discount, UnitPrice and TotalPrice are related in sometimes surprising ways.
After a while, all unit tests ran succesfully for the single flow. Also changes via the standard Salesforce UI were handled correctly. But one thing was wrong: when updating an OpportunityLineItem Quantity via a custom-made LWC, the UnitPrice was changed instead of the TotalPrice.
I did not understand this and I could not create a unit test replicating this behavior. What was the problem?