CodeCov showing impossible drops in coverage

I’ve been seeing bizarre changes in total coverage during PRs and I can’t find any reason behind them. This is the simplest example I’ve come across:

I added 3 lines, which have coverage. But I get a 2% drop in coverage on the file. How is this type of thing possible?

Hi @travisgroth

This is usually due to Cpdecov picking the wrong base for the PR. If you click the commits tab of the PR on Codecov, is the base commit the one you expect?

You can use the -N flag of the bash uploader to specify the base commit in the cases we get it wrong.

Hi @travisgroth

I apologize, there was some confusion about how -N works, including myself, so I’ve given out some bad information.

The -N flag allows you to set the parent commit, not the base commit, as I believed. This means it’s not helpful in overriding our automatic PR base picking system.

I believe the ability to override this is a feature request at this point, I am double-checking with product and engineering to see if there is a current way about this.