TestCase.php

<?php

abstract class TestCase extends \Tester\TestCase
{
    private $tearDownCallbacks = [];

    protected function addTearDownCallback($callback)
    {
        if (!is_callable($callback)) {
            throw new \InvalidArgumentException('$callback is not callable');
        }

        $this->tearDownCallbacks[] = $callback;
    }

    protected function tearDown()
    {
        parent::tearDown();

        foreach ($this->tearDownCallbacks as $callback) {
            $callback();
        }
    }
}

TestWithMockista.php

<?php

trait TestWithMockista
{
    /**
     * @var Registry
     */
    private $mockista;

    /**
     * @return Registry
     */
    protected function getMockista()
    {
        if ($this->mockista === null) {
            $this->mockista = new Registry();
            $this->addTearDownCallback(function () {
                $this->mockista->assertExpectations();
            });
        }

        return $this->mockista;
    }

    protected abstract function addTearDownCallback($callback);
}