Drying Out Specs With Shared Examples


I generally find that most developers are fairly aware of and willing to apply the DRY principal on their main codebase. However, when I look through people’s tests, I find that the old copy/paste habit has found it’s way into their workflow (again?).

I’m using “their code” to save face here…I found this in my own code and started looking for ways to clean it up.

So, let’s take a look at an example of how we can remove some duplication from our specs. This example will be very basic to illustrate the point, but a quick google search for rspec + "shared_examples_for" should turn up some more detailed examples if you’re interested.

Let’s Create a Simple Class

We start with a few simple tests

Now we create a class to make those tests pass

Adding Validation

Now we want our class to validate that name and description are supplied. As good RGR devs, we start by adding the new tests.

Now we see the tests fail, so far so good. There are number of ways to do this kind of validation, but ActiveModel seems to handle this well, and really who wants to write a bunch of validation code? So let’s use the ActiveModel::Validations module.

We start by adding “activemodel” to our gem file (skip this step if you’re using rails).

Now we add the code to make the tests pass

OK, Tests are Passing…

If we look at the specs for the #name and #description properties, we see that they’re essentially the same. Knowing that we might have more properties on this class, we can setup our future selves for success by removing this duplication now.

Developers, when you see this, rather than adding a comment stating that you know it’s a problem…fix it! – You and your whole team will be happier if everyone just does this.

For this step, we’re going to create a set of shared examples that can be applied to any describe/context block.

And there you have it. Running the tests again will show that the tests still pass. The shared_examples_for/it_should_behave_like construct can be really useful for drying out your specs.

We’ve now removed some duplication. Where else could we do this?

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