Are you tired of struggling with mock objects in your unit tests? Do you find yourself wondering how to set an EXPECT_CALL on a mock object that’s just been created? Look no further! In this comprehensive guide, we’ll delve into the world of Google Test and explore the art of setting EXPECT_CALL on a freshly minted mock object.
What is a Mock Object?
In the realm of unit testing, a mock object is a simulated object that mimics the behavior of a real object. Mock objects are used to isolate dependencies and focus on the unit under test. By using mock objects, you can control the inputs and outputs of your system, making it easier to write predictable and reliable unit tests.
Why Do We Need Mock Objects?
- Dependency Isolation**: Mock objects help you isolate dependencies, making it easier to test individual units without affecting other parts of the system.
- Predictable Behavior**: Mock objects allow you to control the behavior of dependencies, ensuring that your tests produce consistent results.
- Faster Testing**: Mock objects reduce the complexity of your tests, making them faster and more efficient.
The EXPECT_CALL Macro
The EXPECT_CALL macro is a powerful tool in Google Test that allows you to specify the expected behavior of a mock object. By setting an EXPECT_CALL, you can define the expected interactions between your system under test and the mock object.
EXPECT_CALL(mock_object, method(CallArgs))
.Times(1)
.WillOnce(ReturnValue);
In the above example, the EXPECT_CALL macro is used to specify that the method function will be called once on the mock_object with the specified CallArgs. The WillOnce clause specifies the return value of the method call.
Setting EXPECT_CALL on a Newly Created Mock Object
Now that we’ve covered the basics, let’s dive into the main event! To set an EXPECT_CALL on a newly created mock object, follow these steps:
- Create a Mock Object**: Create a mock object using the MOCK_METHOD macro:
MOCK_METHOD(object, method, (CallArgs), (override)) { // implementation }; - Declare the Mock Object**: Declare the mock object in your test:
NiceMock<MockObject> mock_object; - Set the EXPECT_CALL**: Use the EXPECT_CALL macro to specify the expected behavior of the mock object:
EXPECT_CALL(mock_object, method(CallArgs)) .Times(1) .WillOnce(ReturnValue); - Use the Mock Object in Your Test**: Use the mock object in your test as you would with a real object:
SystemUnderTest system_under_test(mock_object); system_under_test.doSomething();
Example Code
class MockObject {
public:
MOCK_METHOD(GetValue, (int), (override));
};
TEST(MockObjectTest, GetValueCalledOnce) {
NiceMock<MockObject> mock_object;
EXPECT_CALL(mock_object, GetValue(5))
.Times(1)
.WillOnce(Return(10));
SystemUnderTest system_under_test(mock_object);
int result = system_under_test.doSomething();
ASSERT_EQ(10, result);
}
Tips and Tricks
NiceMock vs Mock
When declaring a mock object, you can choose between using Mock<> or NiceMock<>. The main difference is that NiceMock<> allows for more flexible mocking, while Mock<> is more restrictive.
EXPECT_CALL Order Matters
When setting multiple EXPECT_CALLs, the order in which they are defined matters. EXPECT_CALLs are matched in the order they are specified, so make sure to define them in the correct order.
Use Mock Objects Wisely
Mock objects should be used sparingly and only when necessary. Overusing mock objects can lead to fragile and hard-to-maintain tests. Always strive to write tests that are as close to the real system as possible.
Conclusion
Setting an EXPECT_CALL on a newly created mock object is a crucial step in writing effective unit tests. By following the steps outlined in this guide, you’ll be well on your way to mastering the art of mock objects and Google Test. Remember to use mock objects wisely, and always keep your tests as simple and realistic as possible.
| Keyword | Frequency |
|---|---|
| EXPECT_CALL | 7 |
| Mock Object | 5 |
| Google Test | 3 |
We hope this article has been informative and helpful. Don’t forget to share your experiences and tips in the comments below!
Frequently Asked Question
Get ready to master the art of setting EXPECT_CALL to a mock object!
Q1: What is the correct way to set an EXPECT_CALL to a mock object that is just created?
To set an EXPECT_CALL to a mock object, you need to use the EXPECT_CALL macro provided by Google Mock. The syntax is EXPECT_CALL(mock_object, method). Times(number_of_calls). Here, ‘mock_object’ is the object you want to mock, ‘method’ is the method you want to mock, and ‘number_of_calls’ is the number of times you expect the method to be called.
Q2: What if I want to set an EXPECT_CALL to a mock object that is created dynamically?
If the mock object is created dynamically, you won’t be able to set an EXPECT_CALL to it using the EXPECT_CALL macro directly. Instead, you can use the ON_CALL macro to set the default behavior of the mock object, and then use the EXPECT_CALL macro to set the expectations for specific calls.
Q3: Can I set multiple EXPECT_CALL to the same mock object?
Yes, you can set multiple EXPECT_CALL to the same mock object. The EXPECT_CALL macro is cumulative, meaning that each call to EXPECT_CALL adds to the expectations set by previous calls. So, you can set multiple EXPECT_CALL to the same mock object to specify different expectations for different calls.
Q4: What happens if I set an EXPECT_CALL to a mock object that is not used in the test?
If you set an EXPECT_CALL to a mock object that is not used in the test, the test will fail. This is because the EXPECT_CALL macro specifies that the mock object is expected to be called, but since the object is not used in the test, the expectation will not be met.
Q5: Can I use EXPECT_CALL with a mock object that is created using a factory method?
Yes, you can use EXPECT_CALL with a mock object that is created using a factory method. Just make sure to pass the mock object to the factory method, and then use the EXPECT_CALL macro to set the expectations for the mock object.
