No stack trace shown for previous exceptions during bootstrap

[Steveb-p]

Q	A
PHPUnit version	9.6.7
PHP version	7.4.33
Installation Method	Composer

Summary

I had a situation where the actual error during bootstrap was hidden inside an exception set as $previous, leaving me with only a vague general error (that was coming from my own code, but the actual error with proper stacktrace was inside).

This follows up on #4877 and #4878.

No idea if the behavior is changed for PHPUnit 10.

Current behavior

Currently errors during bootstrap do print stacktrace, but only from the top-most exception.

 Error in bootstrap script: PHPUnit\TestFixture\MyException:
 Big boom. Big bada boom.
 #0 /home/pniedzielski/PhpstormProjects/phpunit/src/Util/FileLoader.php(66): include_once()
 #1 /home/pniedzielski/PhpstormProjects/phpunit/src/Util/FileLoader.php(49): PHPUnit\Util\FileLoader::load()
 #2 /home/pniedzielski/PhpstormProjects/phpunit/src/TextUI/Command.php(565): PHPUnit\Util\FileLoader::checkAndLoad()
 #3 /home/pniedzielski/PhpstormProjects/phpunit/src/TextUI/Command.php(402): PHPUnit\TextUI\Command->handleBootstrap()
 #4 /home/pniedzielski/PhpstormProjects/phpunit/src/TextUI/Command.php(112): PHPUnit\TextUI\Command->handleArguments()
 #5 /home/pniedzielski/PhpstormProjects/phpunit/src/TextUI/Command.php(97): PHPUnit\TextUI\Command->run()
 #6 Standard input code(11): PHPUnit\TextUI\Command::main()
 #7 {main}

How to reproduce

Create a bootstrap file that throws an exception with the 3rd argument ($previous) filled with yet another exception.

Expected behavior

Ideally, the previous exceptions stacktrace is printed out, until we reach the end of the "exception stack".

Something along the lines of:

 Error in bootstrap script: PHPUnit\TestFixture\MyException:
 Big boom. Big bada boom.
 #0 /home/pniedzielski/PhpstormProjects/phpunit/src/Util/FileLoader.php(66): include_once()
 #1 /home/pniedzielski/PhpstormProjects/phpunit/src/Util/FileLoader.php(49): PHPUnit\Util\FileLoader::load()
 #2 /home/pniedzielski/PhpstormProjects/phpunit/src/TextUI/Command.php(565): PHPUnit\Util\FileLoader::checkAndLoad()
 #3 /home/pniedzielski/PhpstormProjects/phpunit/src/TextUI/Command.php(402): PHPUnit\TextUI\Command->handleBootstrap()
 #4 /home/pniedzielski/PhpstormProjects/phpunit/src/TextUI/Command.php(112): PHPUnit\TextUI\Command->handleArguments()
 #5 /home/pniedzielski/PhpstormProjects/phpunit/src/TextUI/Command.php(97): PHPUnit\TextUI\Command->run()
 #6 Standard input code(11): PHPUnit\TextUI\Command::main()
 #7 {main}
 
 Previous exception: Exception:
 Previous boom.
 #0 /home/pniedzielski/PhpstormProjects/phpunit/src/Util/FileLoader.php(66): include_once()
 #1 /home/pniedzielski/PhpstormProjects/phpunit/src/Util/FileLoader.php(49): PHPUnit\Util\FileLoader::load()
 #2 /home/pniedzielski/PhpstormProjects/phpunit/src/TextUI/Command.php(565): PHPUnit\Util\FileLoader::checkAndLoad()
 #3 /home/pniedzielski/PhpstormProjects/phpunit/src/TextUI/Command.php(402): PHPUnit\TextUI\Command->handleBootstrap()
 #4 /home/pniedzielski/PhpstormProjects/phpunit/src/TextUI/Command.php(112): PHPUnit\TextUI\Command->handleArguments()
 #5 /home/pniedzielski/PhpstormProjects/phpunit/src/TextUI/Command.php(97): PHPUnit\TextUI\Command->run()
 #6 Standard input code(11): PHPUnit\TextUI\Command::main()
 #7 {main}