Add in-tree mspec and ruby/spec

* For easier modifications of ruby/spec by MRI developers.
* .gitignore: track changes under spec.
* spec/mspec, spec/rubyspec: add in-tree mspec and ruby/spec.
  These files can therefore be updated like any other file in MRI.
  Instructions are provided in spec/README.
  [Feature #13156] [ruby-core:79246]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58595 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

spec/rubyspec/core/kernel/String_spec.rb

@@ -0,0 +1,106 @@
+require File.expand_path('../../../spec_helper', __FILE__)
+require File.expand_path('../fixtures/classes', __FILE__)
+
+describe :kernel_String, shared: true do
+  it "converts nil to a String" do
+    @object.send(@method, nil).should == ""
+  end
+
+  it "converts a Float to a String" do
+    @object.send(@method, 1.12).should == "1.12"
+  end
+
+  it "converts a boolean to a String" do
+    @object.send(@method, false).should == "false"
+    @object.send(@method, true).should == "true"
+  end
+
+  it "converts a constant to a String" do
+    @object.send(@method, Object).should == "Object"
+  end
+
+  it "calls #to_s to convert an arbitrary object to a String" do
+    obj = mock('test')
+    obj.should_receive(:to_s).and_return("test")
+
+    @object.send(@method, obj).should == "test"
+  end
+
+  it "raises a TypeError if #to_s does not exist" do
+    obj = mock('to_s')
+    class << obj
+      undef_method :to_s
+    end
+
+    lambda { @object.send(@method, obj) }.should raise_error(TypeError)
+  end
+
+  # #5158
+  it "raises a TypeError if respond_to? returns false for #to_s" do
+    obj = mock("to_s")
+    class << obj
+      def respond_to?(meth, include_private=false)
+        meth == :to_s ? false : super
+      end
+    end
+
+    lambda { @object.send(@method, obj) }.should raise_error(TypeError)
+  end
+
+  it "raises a TypeError if #to_s is not defined, even though #respond_to?(:to_s) returns true" do
+    # cannot use a mock because of how RSpec affects #method_missing
+    obj = Object.new
+    class << obj
+      undef_method :to_s
+      def respond_to?(meth, include_private=false)
+        meth == :to_s ? true : super
+      end
+    end
+
+    lambda { @object.send(@method, obj) }.should raise_error(TypeError)
+  end
+
+  it "calls #to_s if #respond_to?(:to_s) returns true" do
+    obj = mock('to_s')
+    class << obj
+      undef_method :to_s
+      def method_missing(meth, *args)
+        meth == :to_s ? "test" : super
+      end
+    end
+
+    @object.send(@method, obj).should == "test"
+  end
+
+  it "raises a TypeError if #to_s does not return a String" do
+    (obj = mock('123')).should_receive(:to_s).and_return(123)
+    lambda { @object.send(@method, obj) }.should raise_error(TypeError)
+  end
+
+  it "returns the same object if it is already a String" do
+    string = "Hello"
+    string.should_not_receive(:to_s)
+    string2 = @object.send(@method, string)
+    string.should equal(string2)
+  end
+
+  it "returns the same object if it is an instance of a String subclass" do
+    subklass = Class.new(String)
+    string = subklass.new("Hello")
+    string.should_not_receive(:to_s)
+    string2 = @object.send(@method, string)
+    string.should equal(string2)
+  end
+end
+
+describe "Kernel.String" do
+  it_behaves_like :kernel_String, :String, Kernel
+end
+
+describe "Kernel#String" do
+  it_behaves_like :kernel_String, :String, Object.new
+
+  it "is a private method" do
+    Kernel.should have_private_instance_method(:String)
+  end
+end