Inconsistent result when calling $this->dotenv->load() multiple times from PHPUnit

[bilogic]

https://gist.github.com/bilogic/4114836067651905888abd542becee55

I have a set of flaky tests in the gist above. What I can't understand is:

1. If the tests are ran individually, they all pass
2. If PHPUnit is used to run them all, test_Can_detect_missing_mandatory_environment_keys fails and it is due to $this->dotenv->load(); returning an empty array here https://gist.github.com/bilogic/4114836067651905888abd542becee55#file-envchecker-php-L61
3. If I re-order test_Can_detect_missing_mandatory_environment_keys as the first test, it passes and now test_Can_parse_environment_file fails due to the same issue of an empty array

Any idea what I'm missing here?