在MSTest中，Assert.Fail中的第二个参数做什么？

import org.easymock.EasyMock;
import org.junit.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.api.easymock.PowerMock;
import org.powermock.core.classloader.annotations.PowerMockIgnore;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;
import org.springframework.aop.framework.Advised;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.util.ReflectionTestUtils;

@RunWith(PowerMockRunner.class)
@PrepareForTest( { PaymentReconService.class })
@PowerMockIgnore(“org.apache.log4j.*”)
public class PaymentGatherServiceTest extends PaymentServiceTestBase {

@Autowired
private GatherService gatherResultService;
@Autowired
private PaymentBaseDAO baseDAO;

/**
* 测试正常postback
*/
public void testPaymentSucc() {
PaymentReconService mock = mock();

Long pbId = 10004L;
String pbStatus = PaymentBaseEO.PB_STATUS_GATHER_SUCC;
BigDecimal succAmount = new BigDecimal(“99.3”);

try {
GatherOrderRO ro = gatherResultService.processPaymentGather(pbId, pbStatus, succAmount, succAmount);
assertNotNull(ro);

} catch (SystemException e) {
fail(e.getLocalizedMessage());
} catch (BusinessException e) {
fail(e.getBusinessCode());
}
EasyMock.verify(mock);
}

/**
* MOCK PaymentReconService实现
* @return
*/
private PaymentReconService mock() {
PaymentReconRO mockRO = new PaymentReconRO(PaymentReconRO.Status.SUCESS, “OK”);