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@adkron /bdd.rb
Created Apr 16, 2014

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class Fifo
EmptyError = Class.new(Exception)
Node = Struct.new(:value, :next)
attr_accessor :size, :top
private :size=, :top=
def initialize
self.size = 0
self.top = nil
end
def empty?
size.zero?
end
def pop
raise EmptyError if empty?
self.size = size - 1
value, self.top = top.value, top.next
value
end
def push(element)
self.size = size + 1
self.top = Node.new(element, top)
end
end
describe Fifo do
context "when it is new" do
it do
is_expected.to be_empty
end
specify do
expect(subject.size).to be_zero
end
specify do
expect{ subject.pop }.to raise_error Fifo::EmptyError
end
specify do
expect{ subject.push :element }.to change{ subject.size }.by(1)
end
end
context "with one element" do
before do
subject.push :element
end
it do
is_expected.to_not be_empty
end
specify do
expect(subject.size).to eql(1)
end
describe "popping an element" do
specify do
expect{ subject.pop }.to change{ subject.size }.by(-1)
end
specify do
expect(subject.pop).to eql(:element)
end
end
end
context "with more than one element" do
before do
subject.push :first_element
subject.push :second_element
end
specify do
expect(subject.pop).to eql(:second_element)
end
specify do
subject.pop
expect(subject.pop).to eql(:first_element)
end
end
end
__END__
push
pop
empty
top
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