Question

This has always bothered me. Why is it people say to unit test in rspec but integration test in cucumber? I am not asking why these tests are necessary – I know what the difference is between integration and unit testing. I just don’t see why, given cucumber’s completely customizable syntax, it isn’t used for unit testing?

It seems to me like the same amount of code is written for cucumber and rspec, the only difference is that for cucumber you separate the test logic from the test writing.

Answer 1

There is quite a lot of overhead in using cucumber for unit testing. Not only you have to write the features but then map them to the implementation using a separate bit of code.

Unit testing is meant to be very fast to write and very fast to execute. Naturally, cucumber focuses on end user experience, mainly due to the language used in writing a feature.

Just to refresh, a feature would contain the following:

As some stakeholder of a system
I would like to perform an activity
So that I can get some benefit out of it

Given a precondition
When I perform an action
Then something should happen

The opening paragraph, that is often ignored, is very important as it sets a context for the operation and explains why something happens. Because of the use of natural language, these things are easy to show to non-programmers in order to get some feedback.

Now, using these for unit tests would seem awkward at best. First of all, the end user focus suggests a more integration approach as the feature says nothing about mocks and UI/logic separation. I.e. a feature like the following just seems weird:

Given a that a database mock is configured with the following data
| ID  | Username |
| 0   | igor     |
When call FindAll on User Repository
Then I get the following user back
| ID  | Username |
| 0   | igor     |

Also, as your SUT gets smaller (i.e. a class), the context of operation is not as important. A User repository does not care about the context e.g. it doesn’t care if the consumer of it is a normal user or a VIP user. A simple component (which it should be, following SRP), is completely deterministic based on its inputs.

So, the unit test is there to validate that what you wrote is correct, and the cucmber test is there to validate that what you wrote satisfies some higher purpose by putting a behavior of the system in a context.