Sadly hasn’t fixed this issue. I’m getting fairly consistent failures for those 4 tests running using docker_test or docker_dev:
These are the same ones that seem to fail a lot on Travis, but I can’t pinpoint exactly why. I can’t repro the failures consistently enough to try and fix it either… 
I wonder whether it’s something to do with Disk i/o speed, as that would explain why I have issues on mac, but @LeoMcA is fine on Linux (mac docker volume mounts are a bit rubbish). I would also imagine that Travis’s disk i/o performance isn’t great. That’s purely speculation though - I have no evidence.
Running stuff natively on my mac, without Docker, is absolutely fine. That’s how I’m doing development at the moment.