gem install rspec # for rspec-core, rspec-expectations, rspec-mocks gem install rspec-core # for rspec-core only
rspec-core provides the structure for writing executable examples of how your code should behave. It 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."
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 ))) order.total.should eq(Money.new(5.55, :USD)) end end
describe method creates an ExampleGroup. Within the
block passed to
describe you can declare examples using the
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 nested groups using the
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
You can declare example groups using either
describe is available at the top level.
You can declare examples within a group using any of
shared examples and contexts
Declare a shared example group using
shared_examples, and then include it
in any group using
shared_examples "collections" do |collection_class| it "is empty when first created" do collection_class.new.should be_empty end end describe Array do include_examples "collections", Array end 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
let declarations, and nested groups/contexts.
You can also use the names
include_context. These are
pretty much the same as
more accurate naming for in which you share hooks,
let declarations, helper
methods, etc, but no examples.
rspec-core stores a metadata hash with every example and group, which contains like 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.metadata[:description].should eq("does something") end
When a class is passed to
describe, you can access it from an example
described_class method, which is a wrapper for
describe Widget do example do described_class.should equal(Widget) end end
This is useful in extensions or shared example groups in which the specific
class is unknown. Taking the shared examples example from above, we can
clean it up a bit using
shared_examples "collections" do it "is empty when first created" do described.new.should be_empty end end describe Array do include_examples "collections" end describe Hash do include_examples "collections" end
When you install the rspec-core gem, it installs the
which you'll use to run rspec. The
rspec comes with many useful options.
rspec --help to see the complete list.
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 describe Calculator do it "add(x,y) returns the sum of its arguments" do Calculator.new.add(1, 2).should eq(3) 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
Implement the simplest solution:
# in lib/calculator.rb class Calculator def add(a,b) a + b end end
Be 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 it pass:
$ rspec spec/calculator_spec.rb . Finished in 0.000315 seconds 1 example, 0 failures
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