Dotnet Test Command Unknown switch, -r

Trying to update a docker container used for testing. I'm trying to pass the -r flag to set the output directory. All of my attempts have been met with:

test_image_1  | MSBUILD : error MSB1001: Unknown switch.
test_image_1  | Switch: -r /app/TestResults

The actual command being run:

ENTRYPOINT ["dotnet", "test",  "-r \"/app/TestResults\"", "-l:trx;verbosity=detailed"]

I've tried with the path unescaped, and I've tried with the -r after the -l. Prior to this it had been using the -l without issue. The docs are not very helpful in that they imply -r some/Path/ is fine.

Per the docs:

-r|--results-directory <RESULTS_DIR>