Don't Overuse Mocks

Mocks are powerful, but easy to abuse.

Bad

TEST_F(PaymentProcessorTest, ShouldChargeCreditCard) {
  PaymentProcessor payment_processor(mock_credit_card_server_);

  InSequence s;
  EXPECT_CALL(mock_credit_card_server_, IsServerAvailable())
      .WillOnce(Return(true));
  EXPECT_CALL(mock_credit_card_server_, BeginTransaction())
      .WillOnce(Return(mock_transaction_manager_));
  EXPECT_CALL(mock_transaction_manager_, GetTransaction())
      .WillOnce(Return(transaction_));
  EXPECT_CALL(mock_credit_card_server_, Pay(transaction_, credit_card_, 500))
      .WillOnce(Return(mock_payment_));
  EXPECT_CALL(mock_payment_, IsOverMaxBalance()).WillOnce(Return(false));

  payment_processor.ProcessPayment(credit_card_, Dollars(500));
}

Overusing mocks makes tests harder to understand, maintain, and provides less insurance that your code is working properly.

If you don't need a mock, don't use one. Understanding when to use a mock comes from understanding what you want to test.

Good

TEST_F(PaymentProcessorTest, ShouldChargeCreditCard) {
  PaymentProcessor payment_processor(credit_card_server_);
  payment_processor.ProcessPayment(credit_card_, Dollars(500));
  EXPECT_EQ(credit_card_server_.GetMostRecentCharge(credit_card_), 500);
}