spec/ruby/core/kernel/define_singleton_method_spec.rb


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require_relative '../../spec_helper'
require_relative 'fixtures/classes'

describe "Kernel#define_singleton_method" do
  describe "when given an UnboundMethod" do
    class DefineSingletonMethodSpecClass
      MY_CONST = 42
      define_singleton_method(:another_test_method, self.method(:constants))
    end

    it "correctly calls the new method" do
      klass = DefineSingletonMethodSpecClass
      klass.another_test_method.should == klass.constants
    end

    it "adds the new method to the methods list" do
      DefineSingletonMethodSpecClass.should have_method(:another_test_method)
    end

    it "defines any Child class method from any Parent's class methods" do
      um = KernelSpecs::Parent.method(:parent_class_method).unbind
      KernelSpecs::Child.send :define_singleton_method, :child_class_method, um
      KernelSpecs::Child.child_class_method.should == :foo
      ->{KernelSpecs::Parent.child_class_method}.should raise_error(NoMethodError)
    end

    it "will raise when attempting to define an object's singleton method from another object's singleton method" do
      other = KernelSpecs::Parent.new
      p = KernelSpecs::Parent.new
      class << p
        def singleton_method
          :single
        end
      end
      um = p.method(:singleton_method).unbind
      ->{ other.send :define_singleton_method, :other_singleton_method, um }.should raise_error(TypeError)
    end

  end

  it "defines a new method with the given name and the given block as body in self" do
    class DefineSingletonMethodSpecClass
      define_singleton_method(:block_test1) { self }
      define_singleton_method(:block_test2, &-> { self })
    end

    o = DefineSingletonMethodSpecClass
    o.block_test1.should == o
    o.block_test2.should == o
  end

  it "raises a TypeError when the given method is no Method/Proc" do
    -> {
      Class.new { define_singleton_method(:test, "self") }
    }.should raise_error(TypeError)

    -> {
      Class.new { define_singleton_method(:test, 1234) }
    }.should raise_error(TypeError)
  end

  it "defines a new singleton method for objects" do
    obj = Object.new
    obj.define_singleton_method(:test) { "world!" }
    obj.test.should == "world!"
    -> {
      Object.new.test
    }.should raise_error(NoMethodError)
  end

  it "maintains the Proc's scope" do
    class DefineMethodByProcClass
      in_scope = true
      method_proc = proc { in_scope }

      define_singleton_method(:proc_test, &method_proc)
    end

    DefineMethodByProcClass.proc_test.should == true
  end

  it "raises an ArgumentError when no block is given" do
    obj = Object.new
    -> {
      obj.define_singleton_method(:test)
    }.should raise_error(ArgumentError)
  end

  it "does not use the caller block when no block is given" do
    o = Object.new
    def o.define(name)
      define_singleton_method(name)
    end

    -> {
      o.define(:foo) { raise "not used" }
    }.should raise_error(ArgumentError)
  end
end