01_Tag.php

<?php

class Tag
{
    public function normalizeName($name)
    {
        $normal = trim($name);
        $normal = strtolower($normal);

        return $normal;
    }
}

02_TagTest.php

<?php

class TagTest extends PHPUnit_Framework_TestCase
{
    /**
     * @covers Tag::normalizeName
     * @dataProvider provideNormalizeName
     */
    public function testNormalizeName($input, $expected)
    {
        $tag = new Tag();
        $this->assertEquals($expected, $tag->normalizeName($input));
    }

    public function provideNormalizeName()
    {
        return array(
            array('foo', 'foo'),
            array('FOO', 'foo'),
            array(' foo ', 'foo'),
            array(' FOO ', 'foo'),
        );
    }
}

03_Tag.php

<?php

class Tag
{
    protected $normalizer;

    public function __construct(Normalizer $normalizer)
    {
        $this->normalizer = $normalizer;
    }

    public function normalizeName($name)
    {
        return $this->normalizer->normalize($name);
    }
}

04_TagTest.php

<?php

class TagTest extends PHPUnit_Framework_TestCase
{
    /**
     * @covers Tag::normalizeName
     */
    public function testNormalizeName()
    {
        $input = 'foo';
        $expected = 'foo';

        // the final "false" tells PHPUnit not to call the Normalizer
        // constructor because it requires another dependency, which we don't
        // care about right now
        $normalizer = $this->getMock('Normalizer', array(), array(), '', false);
        $normalizer
            ->expects($this->once())
            ->method('normalize')
            ->with($input)
            ->will($this->returnValue($expected));

        $tag = new Tag($normalizer);
        $this->assertEquals($expected, $tag->normalizeName($input));
    }
}

05_TagTest.php

<?php

class TagTest extends PHPUnit_Framework_TestCase
{
    /**
     * @covers Tag::normalizeName
     */
    public function testNormalizeName()
    {
        $input = 'foo';
        $expected = 'foo';

        $normalizer = $this->getMockBuilder('Normalizer')
            ->disableOriginalConstructor()
            ->getMock();
        $normalizer
            ->expects($this->once())
            ->method('normalize')
            ->with($input)
            ->will($this->returnValue($expected));

        $tag = new Tag($normalizer);
        $this->assertEquals($expected, $tag->normalizeName($input));
    }
}