How NOT to tests PHP 5.4 traits with PHPUnit.

HashCodeTraitImpl.php

<?php
namespace FlorianWolters\Component\Core;

/**
 * A stub class for {@link HashCodeTraitTest} that uses the trait {@link
 * HashCodeTrait}.
 *
 * @author    Florian Wolters <wolters.fl@gmail.com>
 * @copyright 2012 Florian Wolters
 * @license   http://gnu.org/licenses/lgpl.txt LGPL-3.0+
 * @link      http://github.com/FlorianWolters/PHP-Component-Core-HashCode
 * @see       HashCodeTraitTest
 * @since     Class available since Release 0.1.0
 */
class HashCodeTraitImpl
{
    use HashCodeTrait;
}

HashCodeTraitTest.php

<?php
namespace FlorianWolters\Component\Core;

/**
 * Test class for {@link HashCodeTrait}.
 *
 * @author    Florian Wolters <wolters.fl@gmail.com>
 * @copyright 2012 Florian Wolters
 * @license   http://gnu.org/licenses/lgpl.txt LGPL-3.0+
 * @link      http://github.com/FlorianWolters/PHP-Component-Core-HashCode
 * @since     Class available since Release 0.1.0
 */
class HashCodeTraitTest extends \PHPUnit_Framework_TestCase
{
    /**
     * @var object
     */
    private $traitObject;

    /**
     * Sets up the fixture.
     *
     * This method is called before a test is executed.
     *
     * @return void
     */
    public function setUp()
    {
        $this->traitObject = new HashCodeTraitImpl;
    }

    /**
     * @return void
     *
     * @covers FlorianWolters\Component\Core\HashCodeTrait\hashCode
     * @test
     */
    public function testHashCodeFormat()
    {
        $expected = '/^([0-9a-z]){32}$/';
        $actual = $this->traitObject->hashCode();

        $this->assertRegExp($expected, $actual);
    }

    /**
     * @return void
     *
     * @covers FlorianWolters\Component\Core\HashCodeTrait\hashCode
     * @test
     */
    public function testHashCodeIsSameForSameObject()
    {
        $expected = $this->traitObject->hashCode();
        $actual = $this->traitObject->hashCode();

        $this->assertEquals($expected, $actual);
    }

    /**
     * @return void
     *
     * @covers FlorianWolters\Component\Core\HashCodeTrait\hashCode
     * @test
     */
    public function testHashCodeIsDifferentForDifferentObject()
    {
        $expected = $this->traitObject->hashCode();
        $anotherTraitObject = new HashCodeTraitImpl;
        $actual = $anotherTraitObject->hashCode();

        $this->assertNotEquals($expected, $actual);
    }
}

Since I stumbled on this in google, here's how you test your trait for other people who will end up here:

class HashCodeTraitTest extends TestCase
{
    /**
     * @var HashCodeTrait
     */
    private $traitObject;

    public function setUp()
    {
        $this->traitObject = $this->getMockForTrait(HashCodeTrait::class);
    }

    public function testHashCodeIsSameForSameObject()
    {
        $expected = $this->traitObject->hashCode();
        $actual = $this->traitObject->hashCode();

        $this->assertEquals($expected, $actual);
    }
}