RSpec Expectations 
RSpec::Expectations lets you express expected outcomes on an object in an example.
expect(account.balance).to eq(Money.new(37.42, :USD))Install
If you want to use rspec-expectations with rspec, just install the rspec gem and RubyGems will also install rspec-expectations for you (along with rspec-core and rspec-mocks):
gem install rspec
Want to run against the master branch? You'll need to include the dependent
RSpec repos as well. Add the following to your Gemfile:
%w[rspec-core rspec-expectations rspec-mocks rspec-support].each do |lib|
gem lib, :git => "git://github.com/rspec/#{lib}.git", :branch => 'master'
endIf you want to use rspec-expectations with another tool, like Test::Unit, Minitest, or Cucumber, you can install it directly:
gem install rspec-expectations
Contributing
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.
Basic usage
Here's an example using rspec-core:
RSpec.describe Order do
it "sums the prices of the items in 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 and it methods come from rspec-core. The Order, LineItem, Item and Money classes would be from your code. The last line of the example
expresses an expected outcome. If order.total == Money.new(5.55, :USD), then
the example passes. If not, it fails with a message like:
expected: #<Money @value=5.55 @currency=:USD>
got: #<Money @value=1.11 @currency=:USD>
Built-in matchers
Equivalence
expect(actual).to eq(expected) # passes if actual == expected
expect(actual).to eql(expected) # passes if actual.eql?(expected)
expect(actual).not_to eql(not_expected) # passes if not(actual.eql?(expected))Note: The new expect syntax no longer supports the == matcher.
Identity
expect(actual).to be(expected) # passes if actual.equal?(expected)
expect(actual).to equal(expected) # passes if actual.equal?(expected)Comparisons
expect(actual).to be > expected
expect(actual).to be >= expected
expect(actual).to be <= expected
expect(actual).to be < expected
expect(actual).to be_within(delta).of(expected)Regular expressions
expect(actual).to match(/expression/)Note: The new expect syntax no longer supports the =~ matcher.
Types/classes
expect(actual).to be_an_instance_of(expected) # passes if actual.class == expected
expect(actual).to be_a(expected) # passes if actual.kind_of?(expected)
expect(actual).to be_an(expected) # an alias for be_a
expect(actual).to be_a_kind_of(expected) # another aliasTruthiness
expect(actual).to be_truthy # passes if actual is truthy (not nil or false)
expect(actual).to be true # passes if actual == true
expect(actual).to be_falsy # passes if actual is falsy (nil or false)
expect(actual).to be false # passes if actual == false
expect(actual).to be_nil # passes if actual is nil
expect(actual).to_not be_nil # passes if actual is not nilExpecting errors
expect { ... }.to raise_error
expect { ... }.to raise_error(ErrorClass)
expect { ... }.to raise_error("message")
expect { ... }.to raise_error(ErrorClass, "message")Expecting throws
expect { ... }.to throw_symbol
expect { ... }.to throw_symbol(:symbol)
expect { ... }.to throw_symbol(:symbol, 'value')Yielding
expect { |b| 5.tap(&b) }.to yield_control # passes regardless of yielded args
expect { |b| yield_if_true(true, &b) }.to yield_with_no_args # passes only if no args are yielded
expect { |b| 5.tap(&b) }.to yield_with_args(5)
expect { |b| 5.tap(&b) }.to yield_with_args(Integer)
expect { |b| "a string".tap(&b) }.to yield_with_args(/str/)
expect { |b| [1, 2, 3].each(&b) }.to yield_successive_args(1, 2, 3)
expect { |b| { :a => 1, :b => 2 }.each(&b) }.to yield_successive_args([:a, 1], [:b, 2])Predicate matchers
expect(actual).to be_xxx # passes if actual.xxx?
expect(actual).to have_xxx(:arg) # passes if actual.has_xxx?(:arg)Ranges (Ruby >= 1.9 only)
expect(1..10).to cover(3)Collection membership
expect(actual).to include(expected)
expect(actual).to start_with(expected)
expect(actual).to end_with(expected)
expect(actual).to contain_exactly(individual, items)
# ...which is the same as:
expect(actual).to match_array(expected_array)Examples
expect([1, 2, 3]).to include(1)
expect([1, 2, 3]).to include(1, 2)
expect([1, 2, 3]).to start_with(1)
expect([1, 2, 3]).to start_with(1, 2)
expect([1, 2, 3]).to end_with(3)
expect([1, 2, 3]).to end_with(2, 3)
expect({:a => 'b'}).to include(:a => 'b')
expect("this string").to include("is str")
expect("this string").to start_with("this")
expect("this string").to end_with("ring")
expect([1, 2, 3]).to contain_exactly(2, 3, 1)
expect([1, 2, 3]).to match_array([3, 2, 1])should syntax
In addition to the expect syntax, rspec-expectations continues to support the
should syntax:
actual.should eq expected
actual.should be > 3
[1, 2, 3].should_not include 4See detailed information on the should syntax and its usage.
Compound Matcher Expressions
You can also create compound matcher expressions using and or or:
expect(alphabet).to start_with("a").and end_with("z")
expect(stoplight.color).to eq("red").or eq("green").or eq("yellow")Composing Matchers
Many of the built-in matchers are designed to take matchers as arguments, to allow you to flexibly specify only the essential aspects of an object or data structure. In addition, all of the built-in matchers have one or more aliases that provide better phrasing for when they are used as arguments to another matcher.
Examples
expect { k += 1.05 }.to change { k }.by( a_value_within(0.1).of(1.0) )
expect { s = "barn" }.to change { s }
.from( a_string_matching(/foo/) )
.to( a_string_matching(/bar/) )
expect(["barn", 2.45]).to contain_exactly(
a_value_within(0.1).of(2.5),
a_string_starting_with("bar")
)
expect(["barn", "food", 2.45]).to end_with(
a_string_matching("foo"),
a_value > 2
)
expect(["barn", 2.45]).to include( a_string_starting_with("bar") )
expect(:a => "food", :b => "good").to include(:a => a_string_matching(/foo/))
hash = {
:a => {
:b => ["foo", 5],
:c => { :d => 2.05 }
}
}
expect(hash).to match(
:a => {
:b => a_collection_containing_exactly(
a_string_starting_with("f"),
an_instance_of(Integer)
),
:c => { :d => (a_value < 3) }
}
)
expect { |probe|
[1, 2, 3].each(&probe)
}.to yield_successive_args( a_value < 2, 2, a_value > 2 )Usage outside rspec-core
You always need to load rspec/expectations even if you only want to use one part of the library:
require 'rspec/expectations'Then simply include RSpec::Matchers in any class:
class MyClass
include RSpec::Matchers
def do_something(arg)
expect(arg).to be > 0
# do other stuff
end
end