Environment is not preserved running phpunit with a different user

Problem/Motivation

The documentation on how to run phpunit with a different user on Linux is incorrect.
The exported variables are nor preserved when switching to the different user, so the tests do fail:

Exception: You must provide a SIMPLETEST_BASE_URL environment variable to run some PHPUnit based functional tests.

The documented way:

> export SIMPLETEST_DB='mysql://root@localhost/dev_d8'
> export SIMPLETEST_BASE_URL='http://d8.dev'
> sudo -u www-data ./vendor/bin/phpunit -c core --testsuite functional
> sudo -u www-data ./vendor/bin/phpunit -c core --testsuite functional-javascript

This fails, as the declared environment variables $SIMPLETEST_DB and $SIMPLETEST_BASE_URL are not preserved when switching to www-data. The following command checks for the existence of the environment variables after switching the user:

> export SIMPLETEST_DB='mysql://root@localhost/dev_d8'
> export SIMPLETEST_BASE_URL='http://d8.dev'
> sudo -u www-data printenv | grep 'SIMPLETEST_DB\|SIMPLETEST_BASE_URL'

(Nothing is found)

Proposed resolution

Preserve the environment varibles when switching to the different user:

> export SIMPLETEST_DB='mysql://root@localhost/dev_d8'
> export SIMPLETEST_BASE_URL='http://d8.dev'
> sudo -u www-data -E ./vendor/bin/phpunit -c core --testsuite functional
> sudo -u www-data -E ./vendor/bin/phpunit -c core --testsuite functional-javascript

The following command checks for the existence of the environment variables after switching the user and preserving the environmment:

> export SIMPLETEST_DB='mysql://root@localhost/dev_d8'
> export SIMPLETEST_BASE_URL='http://d8.dev'
> sudo -u www-data -E printenv | grep 'SIMPLETEST_DB\|SIMPLETEST_BASE_URL'
SIMPLETEST_DB=mysql://root@localhost/dev_d8
SIMPLETEST_BASE_URL=http://d8.dev

or more explicit:

> export SIMPLETEST_DB='mysql://root@localhost/dev_d8'
> export SIMPLETEST_BASE_URL='http://d8.dev'
> sudo -u www-data SIMPLETEST_BASE_URL=$SIMPLETEST_BASE_URL SIMPLETEST_DB=$SIMPLETEST_DB ./vendor/bin/phpunit -c core --testsuite functional
> sudo -u www-data SIMPLETEST_BASE_URL=$SIMPLETEST_BASE_URL SIMPLETEST_DB=$SIMPLETEST_DB ./vendor/bin/phpunit -c core --testsuite functional-javascript

The following command checks for the existence of the environment variables after switching the user and explicitly passing the exported environment variables:

> export SIMPLETEST_DB='mysql://root@localhost/dev_d8'
> export SIMPLETEST_BASE_URL='http://d8.dev'
> sudo -u www-data SIMPLETEST_BASE_URL=$SIMPLETEST_BASE_URL SIMPLETEST_DB=$SIMPLETEST_DB printenv | grep 'SIMPLETEST_DB\|SIMPLETEST_BASE_URL'
SIMPLETEST_BASE_URL=http://d8.dev
SIMPLETEST_DB=mysql://root@localhost/dev_d8

Remaining tasks

review

User interface changes

none

API changes

none

Data model changes

none