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Test Driven Development (TDD) for User Interface (UI) with functional tests

Asked 2011-01-11T13:59:47.690
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As we know, TDD means "write the test first, and then write the code". And when it comes to unit-testing, this is fine, because you are limited within the "unit".

However when it comes to UI, writing functional tests beforehand makes less sense (to me). This is because the functional tests have to verify a (possibly long) set of functional requirements. This may usually span multiple screens (pages), preconditions like "logged in", "having recently inserted a record", etc.

According to Wikipedia:

Test-driven development is difficult to use in situations where full functional tests are required to determine success or failure. Examples of these are user interfaces, programs that work with databases, and some that depend on specific network configurations.

(Of course, Wikipedia is no "authority", but this sounds very logical.)

So, any thoughts, or better - experience, with functional tests-first for UI, and then code. Does it work? And is it "pain"?

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2 Answers

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ATDD is very useful if you have a very good grasp on how the UI should behave and also ensure that the cost of change to the functional tests that you build upfront is less.

The biggest problem with doing this, of course, is most often the UI is not fully speced out.

For example, if you are building a product, and are still doing rapid iterations of getting a UI that goes through a usability testing and the feedback incorporated, you do not want the baggage of fixing your functional tests with every small change to the UI.

Given that functional tests are generally slow, the feedback cycle is high and its very painful to keep them green with the changes to UI.

I work on a product team where we had this exact same decision to make. A colleague of mine has summarized our final approach very well here. (Disclaimer: Please ignore the tool specific details there.)

answered 2011-02-27T13:48:08.820
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I've done Acceptance TDD with a UI. We would assert the common header and footer were used via xpath'ing for the appropriate ids. We also used xpath to assert the data appeared in the correct tag relative to whatever ids we used for basic layout and structure. We would also assert the output page is valid html 4.01 strict.

answered 2011-01-11T15:07:31.190

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