<?php 
include 'autoload.php';

class singletonTest extends PHPUnit_Framework_TestCase {
	
	private $voucherInstance;

	public function testGetVoucher() {
	    $this->voucherInstance = new VoucherCheck();
	    $this->assertEquals($this->voucherInstance, new VoucherCheck());
	}
	public function testSignIn() {
	    $this->voucherInstance = new VoucherCheck();
	    $this->assertEquals(null, $this->voucherInstance->signIn());
	}
}

<?php 
include 'autoload.php';

class singletonTest extends PHPUnit_Framework_TestCase {
	
	/**
	 * Voucher instance
	 * 
	 * @var VoucherCheck $voucherInstance
	 */
	private $voucherInstance;

	
	public function testGetVoucher() {
	    $this->voucherInstance = new VoucherCheck();
	    $this->assertEquals($this->voucherInstance, new VoucherCheck());
	}
	public function testSignIn() {
	    $this->voucherInstance = new VoucherCheck();
	    $this->assertEquals(null, $this->voucherInstance->signIn());
	}
}

Add docblock to singleton test
Add docblock to singleton test