Why is cucumber considered an integration testing tool instead of a unit testing tool?

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, giv开发者_如何学Pythonen 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.

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.

Cucumber solves a particular set of problems - engaging business stakeholders who can't easily read code and certainly can't write it, and providing reuse between the steps in automated scenarios. The scenarios also usually cover more than one aspect of behaviour, documenting the functionality of the entire system and often covering whole user journeys across multiple components. The step-based architecture which Cucumber encourages is ideal for handling these scenarios.

It also introduces a whole set of other problems. First, you need to tie the Cucumber scenarios to a set of fixtures, so there's another layer of abstraction which makes them slower to write. Second, English is harder to refactor than code - even with dynamic languages like Ruby (the difference is still more pronounced in the C# and Java variants like JBehave, SpecFlow, Cuke4Nuke and Cuke4Duke). It's harder to tell if steps are still being used, and harder to maintain the scenarios. It's also harder to manage state between the various steps.

With unit tests, the audience is technical. Classes ideally have single responsibilities with little to no duplication, so the reuse of steps isn't important. When we want to change an element of code we tend to look for tests whose naming conventions match the files or classes, so a one-to-one mapping with these is ideal.

Because of Cucumber's overheads, and because we don't get value from the benefits Cucumber provides in return for its overheads, RSpec is a better fit for behaviour at a unit level. (This is also true of JUnit, NUnit, etc.)

If you're missing the "Given, When, Then" of Cucumber, try adding them as comments. This works well for me.

The general idea is that Cucumber tests are written at a higher level than traditional unit tests. For instance when you unit test a particular module you're focused on testing only that modules functionality in isolation away from the rest of the system. The interface into other parts of the system should generally be represented with mock objects.

Cucumber on the other hand focuses on system testing from the UI all the way through the data persistence layer.

Unit testing = Mechanical Engineer testing his new engine in a lab setting mounted on a harness.

Cucumber testing = Test driver putting it on a track for a spin.

Unit tests are to test a particular unit of code in isolation. The usual granularity being a method (or few interacting methods) in a class.

Integration tests are focused on testing many layers of the application stack. For example, you can run an integration test that checks the interaction of you code with a database. Most integration tests focus of two or three layers of objects.

Cucumber tests in particular tend to focus on the full application stack, as they exercise the application by simulating a real user in the interface and all layers of the application, from the UI to the back end services (databases, file system, networks, etc) are in place and used.

Bottom line:

a unit test checks that a particular piece of code abides to its contract with the rest of the world...

Whereas a cucumber test checks the interaction of several pieces of code (a vertical slice some people may say), with the additional beauty that the test itself reads like plain English.

According to Aslak Hellesøy, Cucumber is not a testing tool, rather a collaboration tool (for BDD). He recently posted about this apparent misconception:

https://cucumber.pro/blog/2014/03/03/the-worlds-most-misunderstood-collaboration-tool.html

That said, there are a lot of tests written below the acceptance level that would fall around the integration test layer. Ie,

Given a user at 123 Evergreen Terrace
When I lookup their name
Then I get Homer Simpson

instead of

Given an address
When I lookup a name
Then the home owner name is displayed

It doesn't help that the cukes.info shows as an imperative example (rather than declarative).

Cucumber tests run slow compared to Rspec or Test::Unit or MiniTest unit tests. They have a lot of overhead (it can take minutes to load up the environment, including all the Page Object classes, parse the feature files, and actually execute tests). Running just Cucumber unit tests would be faster than running integration equivalent tests, but not as fast as running something more light weight such as the three above mentioned.

(I am responding to this old question since it was one of the first hits I got when searching for alternatives to Cucumber for integration testing)