First pass at a RubySpec

is_a_spec.rb

require File.expand_path('../../../spec_helper', __FILE__)

describe "Kernel#is_a?" do
  it "returns true when object really is in that class" do
    obj = String.new
    obj.is_a?(String).should be_true
  end

  it "returns true when asked about a superclass" do
    obj = String.new
    obj.is_a?(Object).should be_true
  end

  it "returns false when the object is of another kind" do
    obj = String.new
    obj.is_a?(Fixnum).should be_false
  end

  it "returns false for a sub-class" do
    obj = Object.new
    obj.is_a?(String).should be_false
  end

  it "returns true when asked about a module that is mixed in" do
    module M; end
    class A
      include M
    end

    obj = A.new
    obj.is_a?(M).should be_true
  end

  it "returns false when asked about a module that is not mixed in" do
    module Z; end
    class A
    end

    obj = A.new
    obj.is_a?(Z).should be_false
  end
end