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:
%w[rspec rspec-core rspec-expectations rspec-mocks rspec-support].each do |lib|
gem lib, :git => "https://github.com/rspec/#{lib}.git", :branch => 'main'
endRSpec 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."
RSpec.describe Order do
it "sums the prices of its line items" do
order = Order.new
order.add_entry(LineItem.new(:item => Item.new(
:price => Money.new(1.11, :USD)
)))
order.add_entry(LineItem.new(:item => Item.new(
:price => Money.new(2.22, :USD),
:quantity => 2
)))
expect(order.total).to eq(Money.new(5.55, :USD))
end
endThe 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.
You can also declare nested groups using the describe or context
methods:
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
endNested 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.
Declare a shared example group using shared_examples, and then include it
in any group using include_examples.
RSpec.shared_examples "collections" do |collection_class|
it "is empty when first created" do
expect(collection_class.new).to be_empty
end
end
RSpec.describe Array do
include_examples "collections", Array
end
RSpec.describe Hash do
include_examples "collections", Hash
endNearly 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.
If you want to reuse shared examples or contexts across your RSpec suite you can
define them in a stand alone *.rb files (spec/support/shared_examples/definition.rb
for example). But you will have to manually require them (there is no autoloading of
spec/support/ directory unless you set it up yourself).
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:
it "does something" do |example|
expect(example.metadata[:description]).to eq("does something")
endWhen 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].
RSpec.describe Widget do
example do
expect(described_class).to equal(Widget)
end
endThis 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:
RSpec.shared_examples "collections" do
it "is empty when first created" do
expect(described_class.new).to be_empty
end
end
RSpec.describe Array do
include_examples "collections"
end
RSpec.describe Hash do
include_examples "collections"
endRSpec has two scopes:
- Example Group: Example groups are defined by a
describeorcontextblock, which is eagerly evaluated when the spec file is loaded. The block is evaluated in the context of a subclass ofRSpec::Core::ExampleGroup, or a subclass of the parent example group when you're nesting them. - Example: Examples -- typically defined by an
itblock -- and any other blocks with per-example semantics -- such as abefore(: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:
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
endUnder the covers, this is (roughly) equivalent to:
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
endTo run these examples, RSpec would (roughly) do the following:
example_1 = UsingAnArrayAsAStack.new
example_1.before_example_1
example_1.it_is_initially_empty
example_2 = UsingAnArrayAsAStack::AfterAnItemHasBeenPushed.new
example_2.before_example_1
example_2.before_example_2
example_2.it_allows_the_pushed_item_to_be_poppedWhen 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.
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.
Start with a simple example of behavior you expect from your system. Do this before you write any implementation code:
# in spec/calculator_spec.rb
RSpec.describe Calculator do
describe '#add' do
it 'returns the sum of its arguments' do
expect(Calculator.new.add(1, 2)).to eq(3)
end
end
endRun 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:
# in lib/calculator.rb
class Calculator
def add(a, b)
end
endBe sure to require the implementation file in the spec:
# 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
Failures:
1) Calculator#add returns the sum of its arguments
Failure/Error: expect(Calculator.new.add(1, 2)).to eq(3)
expected: 3
got: nil
(compared using ==)
# ./spec/calculator_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/calculator_spec.rb:5 # Calculator#add returns the sum of its arguments
Implement the simplest solution, by changing the definition of Calculator#add to:
def add(a, b)
a + b
endNow 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.
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