ruby--ruby/spec/ruby/core/hash/slice_spec.rb

require_relative '../../spec_helper'

describe "Hash#slice" do
  before :each do
    @hash = { a: 1, b: 2, c: 3 }
  end

  it "returns a new empty hash without arguments" do
    ret = @hash.slice
    ret.should_not equal(@hash)
    ret.should be_an_instance_of(Hash)
    ret.should == {}
  end

  it "returns the requested subset" do
    @hash.slice(:c, :a).should == { c: 3, a: 1 }
  end

  it "returns a hash ordered in the order of the requested keys" do
    @hash.slice(:c, :a).keys.should == [:c, :a]
  end

  it "returns only the keys of the original hash" do
    @hash.slice(:a, :chunky_bacon).should == { a: 1 }
  end

  it "returns a Hash instance, even on subclasses" do
    klass = Class.new(Hash)
    h = klass.new
    h[:bar] = 12
    h[:foo] = 42
    r = h.slice(:foo)
    r.should == {foo: 42}
    r.class.should == Hash
  end

  it "uses the regular Hash#[] method, even on subclasses that override it" do
    ScratchPad.record []
    klass = Class.new(Hash) do
      def [](value)
        ScratchPad << :used_subclassed_operator
        super
      end
    end

    h = klass.new
    h[:bar] = 12
    h[:foo] = 42
    h.slice(:foo)

    ScratchPad.recorded.should == []
  end
end