Example code:

<?php

class SUT
{
public function foo($a)
{
switch ($a) {
case 'a':
case 'b': // <-- This line is reported not covered but it is
$b = 2;
break;
case 'c':
$b = 3;
break;
default:
$b = 4;
break;
}
return $b;
}
}

class Test extends PHPUnit_Framework_TestCase
{
public function test()
{
$sut = new SUT();
$this->assertEquals(2, $sut->foo('a'));
$this->assertEquals(2, $sut->foo('b'));
$this->assertEquals(3, $sut->foo('c'));
$this->assertEquals(4, $sut->foo('d'));
}
}