Mocking is a crucial aspect of unit testing in software development. It allows developers to simulate the behavior of objects or classes that are not yet fully implemented or are difficult to access. This not only helps in writing better quality code but also saves time by identifying and fixing bugs early on in the development process.
One of the most popular mocking frameworks used in Java is EasyMock. It provides a simple and easy-to-use API for creating mocks and verifying method calls. However, when it comes to mocking genericized classes, EasyMock falls short. This is because genericized classes have type parameters that are not known at runtime, making it difficult to create mocks without getting warning messages.
In this article, we will discuss how to create warningless mocks for genericized classes using EasyMock. But first, let's understand the problem in detail.
When creating a mock for a genericized class, developers face a challenge in specifying the type parameters. EasyMock requires these parameters to create the mock, but since they are not known at runtime, the developer has to use a wildcard or any type as a placeholder. This results in warning messages from the compiler, indicating that the type parameters are not being used properly.
To illustrate this, let's consider a simple example. Suppose we have a genericized class called `ListWrapper` that wraps around a list and provides methods to add and remove items. The class has a type parameter `T` to specify the type of items in the list.
```
public class ListWrapper<T> {
private List<T> list;
public ListWrapper() {
list = new ArrayList<>();
}
public void addItem(T item) {
list.add(item);
}
public void removeItem(T item) {
list.remove(item);
}
}
```
Now, let's try to create a mock for this class using EasyMock:
```
ListWrapper mockListWrapper = EasyMock.createMock(ListWrapper.class);
```
This will result in a warning message from the compiler, indicating that the type parameter `T` is not being used properly. This warning can be suppressed by using `@SuppressWarnings("unchecked")`, but this is not an ideal solution as it hides potential issues in the code.
To overcome this problem, EasyMock provides a solution in the form of `Capture` objects. A `Capture` object is used to capture the arguments passed to a mocked method and can be used to verify the method calls. Using `Capture` objects, we can specify the type parameters for a genericized class without getting any warning messages.
Let's see how this can be applied to our example. First, we create a `Capture` object for the type parameter `T`:
```
Capture<T> capture = EasyMock.newCapture();
```
Next, we use the `andCapture()` method to capture the argument passed to the `addItem()` method:
```
mockListWrapper.addItem(EasyMock.andCapture(capture));
```
Now, when we create the mock, we need to specify the type parameter for the `ListWrapper` class as well as the `Capture` object:
```
ListWrapper<String> mockListWrapper = EasyMock.createMock(ListWrapper.class, capture);
```
This will create the mock without any warning messages. We can then use the `capture.getValue()` method to retrieve the captured argument and verify the method call:
```
String item = capture.getValue();
EasyMock.expectLastCall();
```
Similarly, we can capture the argument for the `removeItem()` method and verify its call as well.
Using `Capture` objects not only helps in creating warningless mocks but also enables us to verify the method calls without relying on specific values. This makes our unit tests more robust and maintainable.
In conclusion, EasyMock provides a simple and effective way to create warningless mocks for genericized classes using `Capture` objects. This not only helps in writing better quality code but also saves time by identifying and fixing potential issues early on in the development process. So next time you come across a warning message while creating mocks for genericized classes, remember to use `Capture` objects and make your unit tests more reliable.
