I have used both fixtures and factories in writing tests. I actually use both currently I use fixtures for my personal project and factories at work. I feel that their can be benefits to both but if I had to go with one I would go with fixtures. It seems to me that you can do everything and more with fixtures. Also your test suite stays a little more organized.
The first question one may ask is what is the difference between a fixture and a factory. Well a fixture is a set of data that is static in nature. This data will get loaded for each test run. A fixture is created using a static file within your testing structure. This is different for each language you use it in. For example in Rails it will be a yaml file while in PHP it’s just an array. This could also depend on the framework your using. If you want the table to start out empty you can create an empty fixture file. Having the static file allows you to setup specific test scenarios. Then you can write your tests around those scenarios and you know the data will always be the same. So if a test shall fail you know it’s not because of a dataset change. In contrast factories create the object and the data at the same time. The database is not stocked with any preloaded data. If you need data for your specific test case you need to call the factory and have it create the data for you. Instead of creating a static file you need to create a factory file. This file will contain the name of the factory and then any custom data you need. Using a factory can have some benefits as you will get random data so your code is being tested against unknown data. Which may be reasonable as you have outside users using your system passing in random sets of data to.
So why do I feel that fixtures are better than factories if fixtures take longer to setup. I find it that factories tend to get messy as you have data objects being created all over your test suite. No factory is identical so you tend to have to work though a lot of different data scenarios. Also if you don’t setup your factory to pass in the proper data you could get false positives. For example maybe your interface validates a field to be one of three values. But you forget to setup your factory with one of those values. Now your tests are failing but the interface and application are running just fine. I suppose you could make the argument you can make the same mistake in a fixture but I feel you have to think about it more as you are filling this data in. Another reason why I don’t think factories are better is they are slower running. For example if you create your fixture files they run once per test run. But they run fast because they don’t have to use active record and create the object. Factories do create an object while creating the data. This takes extra time especially if you have setup a lot of data in your scenario. Another issue I have with using factories is you have to setup your data scenario on each test. You can keep it dry in a way by calling sub classes but again a lot of times you end up just doing factory.new because it’s a one off type of setup. So you tend to duplicate setting up factories a lot especially in a larger development team.
I feel that using either factories or fixtures will be fine. But I feel that fixtures gives you a slight edge for keeping your test suite organized. You are able to write tests against predictable scenarios. Also you are not having to repeat the same datasets over and over again. I feel that this is easier to avoid using fixtures rather than factories.