Ruby on Rails - Why use tests?

I'm confused about what the various testing appliances in Ruby on Rails are for. I have been using the framework for about 6 months but I've never understood the testing part of it. The only testing I've used is JUnit3 in Java and that only briefly.

Everything I've read about it just shows testing validations. Shouldn't the validations in rails just work? It seems more like testing the framework than testing the your code. Why would you need to test validations?

Furthermore, the tests seem super fragile to any change in your code. So if you change anything in your models, you have to change your tests and fixtures to match. Doesn't this violate the DRY principle?

Third, writing test code seems to take alot of time. Is that normal? Wouldn't it just be faster to refresh my browser and see if it worked? I already have to play with my application just to see if it flows correctly and make sure my CSS hasn't exploded. Why wouldn't manual testing be enough?

I've asked these questions before and I haven't gotten more than "automated testing is automated". I am smart enough to figure out the advantages of automating a task. My problem is that costs of writing tests seem absurdly high compared to the benefits. That said, any detailed response is welcome because I probably missed a benefit or two.

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Tests should validate your application logic. Personally, I think my most important tests are the ones I run in Selenium. They check that what shows up in the browser is actually what I expect to see. However, if that's all I had, then I would find it hard to debug - it helps to have lower level tests as well and integration, functional, and unit tests are all useful tools. Unit tests let you check that the model behaves the way you expect it to (and that means every method, not just validatins). Validatins will certainly Just Work, but only if you get them right. If you get them wrong, they will Just Work, but not the way you expected. Writing a couple of lines of test is quicker than debugging later on.

A simple example like the one at http://wiseheartdesign.com/2006/01/16/testing-rails-validations just checks validations in a unit test. The O'Reilly article at http://www.oreillynet.com/pub/a/ruby/2007/06/07/rails-testing-not-just-for-the-paranoid.html?page=1 is a bit more complete (though still fairly basic).

Automated testing is particularly useful in regression testing where you change something and run a suite of tests to check that you didn't break anything else.

Tests are a form of repetition, but they don't violate DRY because they express things in a different way. A test says "I did X so Y should happen". Code says "X happened, so now I need to do Z, which happens to cause Y to happen". i.e. a test stimulates a cause and checks an effect, while code responds to a cause, and effects something.

answered 2008-09-24T12:57:33.383

Ruby on Rails - Why use tests?

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