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rspec-core provides the structure for writing executable examples of how your code should behave, and an rspec command with tools to constrain which examples get run and tailor the output.


gem install rspec      # for rspec-core, rspec-expectations, rspec-mocks
gem install rspec-core # for rspec-core only
rspec --help

Want to run against the main branch? You’ll need to include the dependent RSpec repos as well. Add the following to your Gemfile:

ruby %w[rspec rspec-core rspec-expectations rspec-mocks rspec-support].each do |lib| gem lib, :git => "{lib}.git", :branch => 'main' end

Basic Structure

RSpec uses the words “describe” and “it” so we can express concepts like a conversation:

"Describe an order."
"It sums the prices of its line items."

```ruby RSpec.describe Order do it “sums the prices of its line items” do order =

order.add_entry( =>
  :price =>, :USD)
order.add_entry( =>
  :price =>, :USD),
  :quantity => 2

expect( eq(, :USD))   end end ```

The describe method creates an ExampleGroup. Within the block passed to describe you can declare examples using the it method.

Under the hood, an example group is a class in which the block passed to describe is evaluated. The blocks passed to it are evaluated in the context of an instance of that class.

Nested Groups

You can also declare nested groups using the describe or context methods:

```ruby RSpec.describe Order do context “with no items” do it “behaves one way” do # … end end

context “with one item” do it “behaves another way” do # … end end end ```

Nested groups are subclasses of the outer example group class, providing the inheritance semantics you’d want for free.


You can declare example groups using either describe or context. For a top level example group, describe and context are available off of RSpec. For backwards compatibility, they are also available off of the main object and Module unless you disable monkey patching.

You can declare examples within a group using any of it, specify, or example.

Shared Examples and Contexts

Declare a shared example group using shared_examples, and then include it in any group using include_examples.

```ruby RSpec.shared_examples “collections” do |collection_class| it “is empty when first created” do expect( be_empty end end

RSpec.describe Array do include_examples “collections”, Array end

RSpec.describe Hash do include_examples “collections”, Hash end ```

Nearly anything that can be declared within an example group can be declared within a shared example group. This includes before, after, and around hooks, let declarations, and nested groups/contexts.

You can also use the names shared_context and include_context. These are pretty much the same as shared_examples and include_examples, providing more accurate naming when you share hooks, let declarations, helper methods, etc, but no examples.


rspec-core stores a metadata hash with every example and group, which contains their descriptions, the locations at which they were declared, etc, etc. This hash powers many of rspec-core’s features, including output formatters (which access descriptions and locations), and filtering before and after hooks.

Although you probably won’t ever need this unless you are writing an extension, you can access it from an example like this:

ruby it "does something" do |example| expect(example.metadata[:description]).to eq("does something") end


When a class is passed to describe, you can access it from an example using the described_class method, which is a wrapper for example.metadata[:described_class].

ruby RSpec.describe Widget do example do expect(described_class).to equal(Widget) end end

This is useful in extensions or shared example groups in which the specific class is unknown. Taking the collections shared example group from above, we can clean it up a bit using described_class:

```ruby RSpec.shared_examples “collections” do it “is empty when first created” do expect( be_empty end end

RSpec.describe Array do include_examples “collections” end

RSpec.describe Hash do include_examples “collections” end ```

A Word on Scope

RSpec has two scopes:

  • Example Group: Example groups are defined by a describe or context block, which is eagerly evaluated when the spec file is loaded. The block is evaluated in the context of a subclass of RSpec::Core::ExampleGroup, or a subclass of the parent example group when you’re nesting them.
  • Example: Examples – typically defined by an it block – and any other blocks with per-example semantics – such as a before(:example) hook – are evaluated in the context of an instance of the example group class to which the example belongs. Examples are not executed when the spec file is loaded; instead, RSpec waits to run any examples until all spec files have been loaded, at which point it can apply filtering, randomization, etc.

To make this more concrete, consider this code snippet:

``` ruby RSpec.describe “Using an array as a stack” do def build_stack [] end

before(:example) do @stack = build_stack end

it ‘is initially empty’ do expect(@stack).to be_empty end

context “after an item has been pushed” do before(:example) do @stack.push :item end

it 'allows the pushed item to be popped' do
  expect(@stack.pop).to eq(:item)
end   end end ```

Under the covers, this is (roughly) equivalent to:

``` ruby class UsingAnArrayAsAStack < RSpec::Core::ExampleGroup def build_stack [] end

def before_example_1 @stack = build_stack end

def it_is_initially_empty expect(@stack).to be_empty end

class AfterAnItemHasBeenPushed < self def before_example_2 @stack.push :item end

def it_allows_the_pushed_item_to_be_popped
  expect(@stack.pop).to eq(:item)
end   end end ```

To run these examples, RSpec would (roughly) do the following:

``` ruby example_1 = example_1.before_example_1 example_1.it_is_initially_empty

example_2 = example_2.before_example_1 example_2.before_example_2 example_2.it_allows_the_pushed_item_to_be_popped ```

The rspec Command

When you install the rspec-core gem, it installs the rspec executable, which you’ll use to run rspec. The rspec command comes with many useful options. Run rspec --help to see the complete list.

Store Command Line Options .rspec

You can store command line options in a .rspec file in the project’s root directory, and the rspec command will read them as though you typed them on the command line.

Get Started

Start with a simple example of behavior you expect from your system. Do this before you write any implementation code:

ruby # in spec/calculator_spec.rb RSpec.describe Calculator do describe '#add' do it 'returns the sum of its arguments' do expect(, 2)).to eq(3) end end end

Run this with the rspec command, and watch it fail:

$ rspec spec/calculator_spec.rb ./spec/calculator_spec.rb:1: uninitialized constant Calculator

Address the failure by defining a skeleton of the Calculator class:

ruby # in lib/calculator.rb class Calculator def add(a, b) end end

Be sure to require the implementation file in the spec:

ruby # in spec/calculator_spec.rb # - RSpec adds ./lib to the $LOAD_PATH require "calculator"

Now run the spec again, and watch the expectation fail:

``` $ rspec spec/calculator_spec.rb F


1) Calculator#add returns the sum of its arguments Failure/Error: expect(, 2)).to eq(3)

   expected: 3
        got: nil

   (compared using ==)
 # ./spec/calcalator_spec.rb:6:in `block (3 levels) in <top (required)>'

Finished in 0.00131 seconds (files took 0.10968 seconds to load) 1 example, 1 failure

Failed examples:

rspec ./spec/calcalator_spec.rb:5 # Calculator#add returns the sum of its arguments ```

Implement the simplest solution, by changing the definition of Calculator#add to:

ruby def add(a, b) a + b end

Now run the spec again, and watch it pass:

``` $ rspec spec/calculator_spec.rb .

Finished in 0.000315 seconds 1 example, 0 failures ```

Use the documentation formatter to see the resulting spec:

``` $ rspec spec/calculator_spec.rb –format doc Calculator #add returns the sum of its arguments

Finished in 0.000379 seconds 1 example, 0 failures ```


Once you’ve set up the environment, you’ll need to cd into the working directory of whichever repo you want to work in. From there you can run the specs and cucumber features, and make patches.

NOTE: You do not need to use rspec-dev to work on a specific RSpec repo. You can treat each RSpec repo as an independent project.

Also see