Server-side Java testing with Cactus - JUnit in Action - page 268

Listing 14.4 Minimum code to make the TestAdminServlet compile

[...]
public class AdminServlet extends HttpServlet {

public String getCommand(HttpServletRequest request)
throws ServletException {
return null ;
}
}
This is the minimum code that allows the TestAdminServlet to compile successfully.
The code compiles okay, but there's one more thing that we have to think about.
What you probably notice at this point is that if this test gets executed it will fail,
because of the null object that we return. Tests are used to prevent us from making
mistakes. That said, we always have to ensure that tests fail if we provide corrupt data,
as in the previous example. At this point, we need to ensure that the error is reported
successfully. And after that, when we implement the code under test, the tests should
succeed, and we'll know we've accomplished something. It's a good practice to ensure
that the tests fail when the code fails.

JUnit best practice: always verify that the test fails when it should fail
It's a good practice to always verify that the tests you're writing work. Be sure a
test fails when you expect it to fail. If you're using the test-driven development
methodology, this failure happens as a matter of course. After you write the test,
write a skeleton for the class under test (a class with methods that return null or
throw runtime exceptions). If you try to run your test against a skeleton class, it
should fail. If it doesn't, fix the test (ironically enough) so that it does fail! Even
after the case is fleshed out, you can vet a test by changing an assertion to look
for an invalid value that should cause it to fail.

But let's get back to the test. Listing 14.5 shows the code for getCommand . It's a mini-
mal implementation that passes the tests.

Listing 14.5 Implementation of getCommand that makes the tests pass

[...]
public String getCommand(HttpServletRequest request)
throws ServletException {

String command = request.getParameter(COMMAND_PARAM);

if (command == null ) {
throw new ServletException("Missing parameter ["
+ COMMAND_PARAM + "]");
}
return command;
}
[...]