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 -> { @set.send(@method, 1) }.should raise_error(ArgumentError) -> { @set.send(@method, Object.new) }.should raise_error(ArgumentError) end end