Description:
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I can't find concrete the problem but have errors when trying to use `fastest` (https://github.com/liuggio/fastest) to run parallel phpunit tests. With php7.3 it start to return errcode 1 with some parallel processes.
Windows even does not register these broken executions. I look via AnVir Task Manager / Log. Here I can see list of all executed commands.

Possible problem in work with file handlers. `unlink()` can remove file, which in use by another `proc_open()`, but `fopen()` can't after this create new file.

in vendor/symphony/process/Pipes/WindowsPipes.php:60 for second test fopen($file, 'xb') return null and can't create file, but file at this moment is not exists because was removed by 57 line.

This is new bug. PHP <=7.2 work as expected.


Test script:
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run command in Git's bash:
command: phpunit-tests | head -2 | vendor/bin/fastest --preserve-order -v "phpunit {}"
Where `phpunit-tests` return list of tests.

Expected result:
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Both tests successfully executed.
AnVir Task Manager / Log / record about both executed test commands.


Actual result:
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First test always is broken, but second successfully executed.
AnVir Task Manager / Log / only 1 record about successful executed test command.