This is a configuration flaw in zend-test. It consumes classes from Phpunit 6 but per it's Composer requirements, Phpunit before that version are OK to require:
"phpunit/phpunit": "^4.0 || ^5.0 || ^6.0",
Most likely as your system because of the PHP version does not satisfy the requirements of Phpunit 6, the next lower version was installed.
As the code in the base test case (https://github.com/zendframework/zend-test/blob/master/src/PHPUnit/Controller/AbstractControllerTestCase.php#L444) makes use of Phpunit 6 classes, I strongly assume that when the configuration flaw is made aware to the Zend-Test project, you won't be even able to install on your system any longer.
Therefore upgrade to a recent PHP version and then run
composer update
If you're stuk with the PHP version, downgrade zend-test to a version that supports an older Phpunit version. I don't know that project well, so it's just a suggestion, I don't know if such a version exists or can't even recommend one.
I filed a report, perhaps using that one class was an oversight or there is a less hard way to resolve the dependency: https://github.com/zendframework/zend-test/issues/50