describe :set_difference, shared: true do
  before :each do
    @set = Set[:a, :b, :c]
  end

  it "returns a new Set containing self's elements excluding the elements in the passed Enumerable" do
    @set.send(@method, Set[:a, :b]).should == Set[:c]
    @set.send(@method, [:b, :c]).should == Set[:a]
  end

  it "raises an ArgumentError when passed a non-Enumerable" do
    lambda { @set.send(@method, 1) }.should raise_error(ArgumentError)
    lambda { @set.send(@method, Object.new) }.should raise_error(ArgumentError)
  end
end