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How to test a class that connects to a FTP server?

Asked 2012-03-27T18:48:51.927
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I am developing a live update for my application. So far, I have created almost all unit tests but I have no idea how to test an specific class that connects to a FTP server and downloads new versions.

To test this class, should I create an FTP test server and use it in my unit tests? If so, how can I make sure this FTP server is always consistent to my tests? Should I create manually every file I will need before the test begin or should I automate this in my Test Class (tear down and setup methods)?

This question also applies to unit testing classes that connects do any kind of server.

EDIT

I am already mocking my ftp class so I dont always need to connect to the ftp server in other tests.

Let me see if I got this right about what Warren said in his comment:

I would argue that once you're talking to a separate app over TCP/IP we should call that "integration tests". One is no longer testing a unit or a method, but a system.

When a unit test needs to communicate to another app (that can be a HTTP server or FTP server) is this no longer a unit test but a integration server? If so, am I doing it wrong by trying to use unit testing techniques to create this test? Is it correct to say that I should not unit test this class? It does make sense to me because it seems to be a lot of work for a unit test.

delphi unit-testing ftp delphi-2010
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Write a couple of focused integration tests for the one component which knows how to communicate with an FTP server. For those tests you will need to start an FTP server before each tests, put there any files needed by the test, and after the test shutdown the server.

With that done, in all other tests you won't use the component which really connects to an FTP server, but you will use a fake or mock version of it (which is backed by some in-memory data structure instead of real files and network sockets). That way you can write unit tests, which don't need an FTP server or network connection, for everything else except the FTP client component.

In addition to those tests, it might be desirable to also have some end-to-end tests which launch the whole program (unlike the component-level focused integration tests) and connect a real FTP server. End-to-end tests can't cover all corner cases (unlike unit tests), but they can help to solve integration issues.

answered 2012-03-27T19:13:17.080

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