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Mocks (or I guess fakes, really) can be useful for simulating certain scenarios that are difficult to produce in real life but your code needs to handle. For example if in an integration test you want to see how your application deals with high latency or errors in a service dependency, you can write a mock of that service and have it introduce arbitrary delays or errors.

Of course it helps to test against the real service as well, since it's often prohibitively time-consuming or impossible to model ever aspect of it, but I wouldn't discount mocks so easily.

> I dislike mocks. I've never seen the point in testing code against an entirely fictional representation of the most complicated and slow part of the system, just because it happens to be more convenient.

You aren't testing code against an entirely fictional representation of the system, you are testing one piece of code in isolation, and using a fictional representation of another piece of the system to eliminate variables.

Unit testing is about verifying that individual components do their job correctly -- when doing it, you literally don't care what other pieces of code would do, because that's out of scope of the unit test.

Testing that the whole system works together is system/integration testing, and is a different thing. You don't use mocks for system testing, only unit testing.

> If an app is worth writing, and worth writing tests for, do it justice and test the whole shooting match.

Yes, that's what system/integration testing is for.

That doesn't mean you shouldn't have code that is amenable to proper unit testing.

> otherwise what exactly are you testing?

it depends, what do you want to test ?

If you are testing a single function, why would you care whether the data comes from the database, the network or from a mock ? All you need is to verify that the given function produces the expected output given the right (and wrong) inputs. Being able to test this way also makes easy to keep the components in your software decoupled.

My philosophy is to use mocks for unit tests and the real thing for integration tests.

It seems to me that if you are writing a lot of mocks, you are probably retrofitting tests onto an existing code base. If your code is written to be testable you usually can avoid mocks.

That being said, if you are writing a test on an algorithm and the data comes from a database this means you are not just writing a test on the algorithm - you are writing a test on the database with all the cruft that comes along with that. This test can be hundreds of times slower due to the DB dependency.

So mocks do have their place. The test pyramid is the answer - you need units (sometimes with mocks, integration, system).

In my experience most companies are way too integration heavy and very light on the unit side of things. For example for my current project our dev tests take 12 hours to run. This is the result of going too far away from the unit level and being too integration heavy.

There is a balance! Sounds like the rails world the balance is too unit heavy. In the enterprise world I think it's too integration/system heavy.

I use mocks heavily and I also test the database heavily. I use mocks in unit tests which is part of our automated build process. We also have fixtures and actual db level testing in our second level testing. Why not test both? unit testing will often catch a whole class of errors that integration tests will not or at least not accurately catch. I agree that the TDD dogma is silly but mocks and unit testing have serious value that you seem to be discounting.

Well speed of testing is not the only consideration. Mocks are also (primarily?) intended to isolate your testing so you're not looking through an entire stack to find a bug. Often, especially in early phases of software they're over kill, and distract from implementation time however.

I find stubs occasionally useful. But I don't get mocks.

http://martinfowler.com/articles/mocksArentStubs.html

That's the money link. People who save time by using mocks instead of stubs are deferring design problems to later stages, which is really bad. When I'm only responsible for my module and don't give a shit about the system as a whole, then mocking is fine. But in this case, the development process is toxic.

I dislike mocks too; it introduces a lot of duplication that I think is deeply problematic. Automated tests are for me a way to support changing the system easily and safely; lots of mocks often work against that.

But what you're getting is speed. Tests are at their most valuable when they give you quick feedback. As test suite times creep up, people stop running them as much, or at all. I've been on projects where all our tests run in seconds, and it is an enormously different development experience than when they run in minutes.

Mocks to me represent a different approach to testing - think London School of Testing vs Classic TDD. With Classic TDD, it can be difficult to test side effects in your code since its more focused on input and output.