Effective Testing with RSpec 3

Parts of an Expectation

When you see an expectation like the following one:

10-exploring-rspec-expectations/02/parts_of_an_expectation.rb

expect(deck.cards.count).to eq(52), 'not playing with a full deck'

…you’ll notice several forms of punctuation in use: parentheses, dots, and whitespace. While there’s some variety here, the syntax consistently uses just a few simple parts:

• A subject—the thing you’re testing—that is, an instance of a Ruby class

• A matcher—an object that specifies what you expect to be true about the subject, and provides the pass/fail logic

• (optionally) A custom failure message

These parts are held together with a bit of glue code: expect, together with either the to or not_to method.

Let’s get a feel for how these parts ...