早期获取：《RSpec实用书》开发中版

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"Pragmatic.The RSpec Book.2010.pdf" 是一本仍在开发中的敏捷出版书籍，专为敏捷开发者设计。这本书是作者通过Beta书计划提前发布的，以便读者可以在正式出版前获取到部分内容，从而有机会对书籍的早期版本提供反馈，帮助作者优化和完善。这种方式使得作者和读者都能从中受益。作为Beta版，该书尚未经过全面的技术编辑，因此可能包含错误、排版问题和一些未完成的细节。例如，可能会有语法错误、标点符号不规范、页面布局不合理，比如糟糕的分页、过长的行和不恰当的断字等。这些缺陷并不意味着书籍质量低下，而是在提醒读者这是一本还在不断完善的草稿。尽管存在这些问题，但作者相信读者在阅读过程中仍然会享受到学习的乐趣。在整个过程中，读者可以从作者提供的账户下载更新的PDF版本，以便跟踪最新进展。一旦书籍正式完成并发布，读者将能从同一地址获取最终版及后续的更新内容。这是一本具有实践意义的书籍，主要关注行为驱动开发（BDD）和Ruby的测试框架RSpec与Cucumber。它适合那些想要紧跟敏捷开发潮流，愿意参与书籍早期迭代并贡献反馈的读者。尽管在阅读过程中可能会遇到一些技术上的瑕疵，但对于寻求深入了解这些工具和技术的开发者来说，这无疑是一个难得的机会，可以提前掌握最新知识并参与到其进化过程中。

CUCUMBER 16

While the syntactic details have evolved since Steven’s original version

of RSpec, the basic premise remains. We use RSpec to write executable

examples of the expected behaviour of a small bit of code in a controlled

context. Here’s how that might look:

describe MovieList do

context

"when first created"

"should be empty"

movie_list = MovieList.new

movie_list.should be_empty

end

The it( ) method creates an example of the behaviour of a MovieList, with

the co ntext being that the MovieList was just created. The expression

movie_list.should be_empty should be self-explanatory. Just read it out

loud. You’ll see how be_empty( ) interacts wit h the movie_list in Sec-

tion

11.3, Predicate Matchers, on page 140.

Running this code in a shell with the spec command yields t he following

speciﬁcation:

MovieList when first created

- should be empty

Add some more contexts and examples, and the resulting output looks

even more like a speciﬁcation for a MovieList object:

MovieList when first created

- should be empty

MovieList with 1 item

- should not be empty

- should include that item

Of course, we’re talking about the speciﬁcation of an object, not nec-

essarily a w hole system. You c ould specify application behaviour with

RSpec. Many do. Ideally, however, for specifying application behaviour,

we want something that communicates in broader strokes. And for that,

we use Cucumber.

1.4 Cucumber

Cucumber i s a BDD tool that r eads plain text descriptions of applica-

tion features with example scenarios, and uses the scenario steps to

automate interaction with the code being developed. For example:

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CUCUMBER 17

Cucumber Seeds

Even before we had started exploring structures and syntax

for RSpec, Dan North had been exploring a completely differ-

ent model for a BDD tool. He wanted to document and drive

behaviour in a simpliﬁed language that c ould be easily under-

stood by customers, developers, testers, business analysts, etc ,

etc. The early result of that exploration was the JBehave library,

which is still in active use and development.

Dan ported JBehave to Ruby as RBehave, and we merged it

into RSpec as the Story Runner. It only supported scenarios writ-

ten in Ruby at ﬁrst, but we later added support for plain text,

opening up a whole new world of expressiveness and access.

But as new possibilities were revealed, so were limitations.

In the spring of 2008, Aslak Hellesøy set out to rewrite RSpec’s

Stor y Runner with a real grammar deﬁned with Nathan Sobo’s

Treetop library. Aslak dubbed it Cucumber at the suggestion

of his ﬁancée, Patricia Carrier, thinking it would be a short-lived

working title until it was merged back into RSpec. Little did ei ther

of them know that Cucumber would develop a life of its own.

Line 1

Feature: pay bill on-line

In order to reduce the time I spend paying bills

As a bank customer with a checking account

I want to pay my bills on-line

Scenario: pay a bill

Given checking account with $50

And a payee named Acme

And an Acme bill for $37

When I pay the Acme bill

Then I should have $13 remaining in my checking account

And the payment of $37 to Acme should be listed in Recent Payments

Plain text scenarios like this one are parsed and treated as real code,

providing invaluable beneﬁts like backtraces that emanate from the

plain text steps, and support for multiple languages.

Everything up to and including the Scenario declaration on line 6 is

treated as documentation (not executable). The subsequent lines are

steps in the scenario. In the next chapter, you’ll be writing step def-

initions in Ruby. These step deﬁnitions interact with the code being

developed, and are invoked by Cucumber as it reads in the scenario.

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THE BDD CYCLE 18

Don’t worry if that doesn’t make perfect sense to you just yet. For right

now it’s only important to understand that both RSpec and Cucumber

allow us to specify the behaviour of code with examples that ar e pro-

grammatically tied to the system. The details will become clear as y ou

read on.

1.5 The BDD Cycle

We typically use Cucumber to describe behaviour of the application

from the outside and RSpec to describe the behaviour of its component

parts.

If you’ve ever done TDD before, you’re probably familiar with

the red/green/refactor cycle. With the addition of a higher level tool

like Cucumber, we’ll actually have t wo concentric red/green/refactor

cycles, as depicted in Figure

1.1, on the following page.

Both cycles involve taking small steps and listening to the feedback

you get from the tools. We start with a failing step (red) in Cucumber

(the outer cycle). T o get that step to pass, we’ll drop down to RSpec

(the inner cycle) and drive out the underlying code at a granular level

(red/green/refactor).

At each green point in the RSpec cycle, we’ll check the Cucumber cycle.

If it is sti l l red, the resulting feedback should guide us to the next act i on

in the RSpec cycle. If it is green, we can jump out to Cucumber, refac-

tor if appropriate, and then repeat the cycle by writing a new failing

Cucumber step.

This will all become clear as you read through these chapters.

In the tutorial that follows, we’ll be using a number of features in

Cucumber and RSpec. In most cases w e’ll only touch the surface of

a feature, covering just enough to be able to use it as needed for this

project, with r eferences to oth er places in the book that y ou can go to

learn more of the detail and philosophy behind each f eature.

So now it ’s time to grab some coffee, clear your head, leave your pre-

conceptions at the door and g et ready to get your BDD on. See you

in the next chapter, in which we’ll begin to drive out a command line

version of the classic logic game, Mastermind.

3. Although we use Cuc umber to focus on high level behaviour and RSpec on more

granular aspects of beha viour, each can be used for either purpose.

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