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/string/downcase_spec.rb

@@ -0,0 +1,59 @@
+# -*- encoding: utf-8 -*-
+require File.expand_path('../../../spec_helper', __FILE__)
+require File.expand_path('../fixtures/classes.rb', __FILE__)
+
+describe "String#downcase" do
+  it "returns a copy of self with all uppercase letters downcased" do
+    "hELLO".downcase.should == "hello"
+    "hello".downcase.should == "hello"
+  end
+
+  ruby_version_is ''...'2.4' do
+    it "is locale insensitive (only replaces A-Z)" do
+      "ÄÖÜ".downcase.should == "ÄÖÜ"
+
+      str = Array.new(256) { |c| c.chr }.join
+      expected = Array.new(256) do |i|
+        c = i.chr
+        c.between?("A", "Z") ? c.downcase : c
+      end.join
+
+      str.downcase.should == expected
+    end
+  end
+
+  it "taints result when self is tainted" do
+    "".taint.downcase.tainted?.should == true
+    "x".taint.downcase.tainted?.should == true
+    "X".taint.downcase.tainted?.should == true
+  end
+
+  it "returns a subclass instance for subclasses" do
+    StringSpecs::MyString.new("FOObar").downcase.should be_an_instance_of(StringSpecs::MyString)
+  end
+end
+
+describe "String#downcase!" do
+  it "modifies self in place" do
+    a = "HeLlO"
+    a.downcase!.should equal(a)
+    a.should == "hello"
+  end
+
+  it "returns nil if no modifications were made" do
+    a = "hello"
+    a.downcase!.should == nil
+    a.should == "hello"
+  end
+
+  it "raises a RuntimeError when self is frozen" do
+    lambda { "HeLlo".freeze.downcase! }.should raise_error(RuntimeError)
+    lambda { "hello".freeze.downcase! }.should raise_error(RuntimeError)
+  end
+
+  with_feature :encoding do
+    it "sets the result String encoding to the source String encoding" do
+      "ABC".downcase.encoding.should equal(Encoding::UTF_8)
+    end
+  end
+end