Mocking is a powerful tool in software development, allowing developers to simulate the behavior of objects and methods in order to test their code. One popular mocking framework is Mockito, which allows developers to easily create mock objects for testing.
One common scenario in testing is the need to change the return value of a mock object for future calls. This can be useful when testing different scenarios or when the return value of the method being mocked needs to be dynamic. In this article, we will explore how to change the return value of a Mockito mock object for future calls.
To begin, let's create a simple Java class that we will use for our mock object. We will call this class "Calculator" and it will have a method called "add" which takes in two integers and returns their sum.
```
public class Calculator {
public int add(int a, int b) {
return a + b;
}
}
```
Next, we will create our mock object using Mockito. This can be done by using the static method "mock" from the Mockito class and passing in the class we want to mock.
```
Calculator mockCalculator = Mockito.mock(Calculator.class);
```
Now, let's say we want to change the return value of the "add" method for future calls. We can do this by using the "thenReturn" method from Mockito and passing in the desired return value.
```
Mockito.when(mockCalculator.add(2, 3)).thenReturn(5);
```
In this example, we are telling Mockito that when the "add" method is called with the parameters 2 and 3, it should return 5 instead of the actual sum. This will only affect future calls to the "add" method, not the current one.
We can also use the "thenReturn" method to return different values for different scenarios. For example, if we want the "add" method to return 5 for the first call and 10 for the second call, we can do the following:
```
Mockito.when(mockCalculator.add(2, 3)).thenReturn(5).thenReturn(10);
```
This will return 5 for the first call and 10 for the second call. Any subsequent calls will return the last defined value, in this case, 10.
In addition to using the "thenReturn" method, we can also use the "thenAnswer" method to provide a custom answer for the mock object. This can be useful when the return value needs to be calculated based on the parameters passed to the method.
```
Mockito.when(mockCalculator.add(Mockito.anyInt(), Mockito.anyInt())).thenAnswer(new Answer<Integer>() {
public Integer answer(InvocationOnMock invocation) throws Throwable {
int a = (int) invocation.getArguments()[0];
int b = (int) invocation.getArguments()[1];
return a * b;
}
});
```
In this example, we are using the Mockito "anyInt" matcher to match any integer value passed to the "add" method. Then, in the "thenAnswer" method, we are accessing the parameters passed to the method and returning their product instead of the sum.
It is important to note that changing the return value of a mock object for future calls will only affect the specific method call that was mocked. Any subsequent calls to the same method with different parameters will use the actual return value of the method.
In conclusion, changing the return value of a Mockito mock object for future calls is a useful technique in testing that allows for more dynamic and flexible testing scenarios. By using the "thenReturn" and "thenAnswer" methods, developers can easily customize the behavior of their mock objects and test their code with different scenarios.
