Need info how to run PHPUnit functional tests (BrowserTestCase)

[rpsu]

I can't seem to get the functional PHPUnit tests run without errors. Inside core/phpunit.xml I have set this:
<env name="BROWSERTEST_OUTPUT_DIRECTORY" value="/var/www/html/modules/regcode_simple/phpUnitHTML"/> (where regcode_simple is the module name)

Running tests from the host with
$> .docker/phpunit.sh --group regcode_simple
has mkdir() perm issues:

Running tests from the docker directly with
root@10e9cb3215cf:/var/www/html/core# ../vendor/bin/phpunit --group regcode_simple
fails with connection problem:

[rpsu]

I'll rephrase my self, thanks to very quick (!) responses in Twitter.
Running a single module tests can be done with:
.docker/run-tests.sh --module mymodule

[rpsu]

I added this to README.md via #11 PR