I noticed this when checking build logs for Translate.
10:51:29 1) EscapeCharacterValidatorTest::testEmptyValues 10:51:29 expectExceptionMessageRegExp() is deprecated in PHPUnit 8 and will be removed in PHPUnit 9. 10:51:29 10:51:29 2) EscapeCharacterValidatorTest::testInvalidEscape 10:51:29 expectExceptionMessageRegExp() is deprecated in PHPUnit 8 and will be removed in PHPUnit 9.