External class not found error running LTI unit tests

$ vendor/bin/phpunit mod/lti/tests/locallib_test.php --filter test_lti_get_lti_types_and_proxies_count_type_with_proxyid

Moodle 4.2dev+ (Build: 20230406)

Php: 8.0.28, mysqli: 8.0.32, OS: Linux 5.4.0-146-generic x86_64

PHPUnit 9.5.27 by Sebastian Bergmann and contributors.

E                                                                   1 / 1 (100%)

Time: 00:00.097, Memory: 60.50 MB

There was 1 error:

1) mod_lti\locallib_test::test_lti_get_lti_types_and_proxies_count_type_with_proxyid

Error: Class "external_api" not found

/mnt/export/moodle/master/src/mod/lti/tests/mod_lti_testcase.php:62

/mnt/export/moodle/master/src/mod/lti/tests/locallib_test.php:2152

/mnt/export/moodle/master/src/mod/lti/tests/locallib_test.php:2080

/mnt/export/moodle/master/src/lib/phpunit/classes/advanced_testcase.php:80

ERRORS!

Tests: 1, Assertions: 0, Errors: 1.