public function testUpdate()
{
$agreement = $this->getMock('Magento\\Paypal\\Model\\Billing\\Agreement', [], [], '', false);
$argument = $this->getMock('Magento\\Sales\\Model\\ResourceModel\\Order\\Collection', [], [], '', false);
$this->_registry->expects($this->once())->method('registry')->with('current_billing_agreement')->will($this->returnValue($agreement));
$agreement->expects($this->once())->method('getId')->will($this->returnValue('agreement id'));
$this->_agreementResource->expects($this->once())->method('addOrdersFilter')->with($this->identicalTo($argument), 'agreement id');
$this->assertSame($argument, $this->_model->update($argument));
}
