Testing with mock objects - JUnit in Action - page 107

At B , we use a mock logger that implements the Log interface but does nothing. Next,
we create a MockConfiguration instance C and set it up to return a given SQL query
when Configuration.getSQL is called. Finally, we create the instance of Default-
AccountManager D that we test, passing to it the Log and Configuration instances.
We've been able to completely control our logging and configuration behavior
from outside the code to test, in the test code. As a result, our code is more flexible
and allows for any logging and configuration implementation to be used. You'll see
more of these code refactorings in this chapter and later ones.
One last point to note is that if you write your test first, you'll automatically design
your code to be flexible. Flexibility is a key point when writing a unit test. If you test
first, you won't incur the cost of refactoring your code for flexibility later.

7.4 Mocking an HTTP connection

To see how mock objects work in a practical example, let's use the simple application
that opens an HTTP connection to a remote server and reads the content of a page. In
chapter 6 we tested that application using stubs. Let's now unit test it using a mock
object approach to simulate the HTTP connection.
In addition, you'll learn how to write mocks for classes that don't have a Java inter-
face (namely, the HttpURLConnection class). We show a full scenario in which you
start with an initial testing implementation, improve the implementation as you go,
and modify the original code to make it more flexible. We also show how to test for
error conditions using mocks.
As you dive in, you'll keep improving both the test code and the sample applica-
tion, exactly as you might if you were writing the unit tests for the same application. In
the process, you'll learn how to reach a simple and elegant testing solution while mak-
ing your application code more flexible and capable of handling change.
Figure 7.2 introduces the sample HTTP application.
This application consists of a simple WebClient.getContent method performing
an HTTP connection to a web resource executing on a web server. We want to be able
to unit test the getContent method in isolation from the web resource.

Figure 7.2 The sample HTTP application before introducing the test