Running the full phpunit test set fails at Testing suite core_blog_testsuite.

This seems to be a result of MDL-81520
I tested with all four fixed branches from that issue and it only affects the 401 and 403 branches.

Pretty sure it's just a missing
require_once($CFG->dirroot . '/webservice/tests/helpers.php');

To reproduce:
run vendor/bin/phpunit blog/tests/external/external_test.php

Expected:
OK (52 tests, 262 assertions)

Actual:
PHP Fatal error: Uncaught Error: Class "externallib_advanced_testcase" not found in /var/www/html/blog/tests/external/external_test.php:40
Stack trace:
#0 /var/www/html/vendor/phpunit/phpunit/src/Util/FileLoader.php(66): include_once()
#1 /var/www/html/vendor/phpunit/phpunit/src/Util/FileLoader.php(49): PHPUnit\Util\FileLoader::load('/var/www/html/b...')
#2 /var/www/html/vendor/phpunit/phpunit/src/Runner/StandardTestSuiteLoader.php(43): PHPUnit\Util\FileLoader::checkAndLoad('/var/www/html/b...')
#3 /var/www/html/vendor/phpunit/phpunit/src/Runner/BaseTestRunner.php(146): PHPUnit\Runner\StandardTestSuiteLoader->load('/var/www/html/b...')
#4 /var/www/html/vendor/phpunit/phpunit/src/Runner/BaseTestRunner.php(112): PHPUnit\Runner\BaseTestRunner->loadSuiteClass('/var/www/html/b...')
#5 /var/www/html/vendor/phpunit/phpunit/src/TextUI/Command.php(121): PHPUnit\Runner\BaseTestRunner->getTest('/var/www/html/b...', Array)
#6 /var/www/html/vendor/phpunit/phpunit/src/TextUI/Command.php(97): PHPUnit\TextUI\Command->run(Array, true)
#7 /var/www/html/vendor/phpunit/phpunit/phpunit(98): PHPUnit\TextUI\Command::main()
#8 /var/www/html/vendor/bin/phpunit(122): include('/var/www/html/v...')
#9 {main}