TextUI TestRunner cannot run a non-TestSuite Test instance

[BHSPitMonkey]

Q	A
PHPUnit version	7.3
PHP version	7.1
Installation Method	Composer

$ composer info | sort
brianium/habitat                   v1.0.0 A dependable php environment
brianium/paratest                  2.0    Parallel testing for PHP
composer/semver                    1.4.2  Semver library that offers util...
doctrine/instantiator              1.1.0  A small, lightweight utility to...
myclabs/deep-copy                  1.8.1  Create deep copies (clones) of ...
phar-io/manifest                   1.0.3  Component for reading phar.io m...
phar-io/version                    2.0.1  Library for handling version in...
phpdocumentor/reflection-common    1.0.1  Common reflection classes used ...
phpdocumentor/reflection-docblock  4.3.0  With this component, a library ...
phpdocumentor/type-resolver        0.4.0 
phpspec/prophecy                   1.8.0  Highly opinionated mocking fram...
phpunit/php-code-coverage          6.0.7  Library that provides collectio...
phpunit/php-file-iterator          2.0.1  FilterIterator implementation t...
phpunit/php-text-template          1.2.1  Simple template engine.
phpunit/php-timer                  2.0.0  Utility class for timing
phpunit/php-token-stream           3.0.0  Wrapper around PHP's tokenizer ...
phpunit/phpunit                    7.3.1  The PHP Unit Testing framework.
sebastian/code-unit-reverse-lookup 1.0.1  Looks up which function or meth...
sebastian/comparator               3.0.2  Provides the functionality to c...
sebastian/diff                     3.0.1  Diff implementation
sebastian/environment              3.1.0  Provides functionality to handl...
sebastian/exporter                 3.1.0  Provides the functionality to e...
sebastian/global-state             2.0.0  Snapshotting of global state
sebastian/object-enumerator        3.0.3  Traverses array structures and ...
sebastian/object-reflector         1.1.1  Allows reflection of object att...
sebastian/recursion-context        3.0.0  Provides functionality to recur...
sebastian/resource-operations      1.0.0  Provides a list of PHP built-in...
sebastian/version                  2.0.1  Library that helps with managin...
symfony/console                    v4.1.3 Symfony Console Component
symfony/polyfill-mbstring          v1.9.0 Symfony polyfill for the Mbstri...
symfony/process                    v4.1.3 Symfony Process Component
theseer/tokenizer                  1.1.0  A small library for converting ...
webmozart/assert                   1.3.0  Assertions to validate method i...

It seems that TextUI/TestRunner::doRun has an issue when passed an object that isn't a TestSuite. If the constructor argument to run is a non-TestSuite Test object, things start to break beginning with a call to $this->processSuiteFilters, (https://github.com/sebastianbergmann/phpunit/blob/master/src/TextUI/TestRunner.php#L158) which expects a TestSuite instance.

This is at odds with the TestRunner::doRun type hint (which specifies Test), and the TestRunner::run function itself (which appears to accept Test instances by design). This also means that the Example 12.5 in the manual (https://phpunit.readthedocs.io/en/7.3/extending-phpunit.html#implement-phpunit-framework-test) cannot actually work.