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/array/unshift_spec.rb

@@ -0,0 +1,50 @@
+require File.expand_path('../../../spec_helper', __FILE__)
+require File.expand_path('../fixtures/classes', __FILE__)
+
+describe "Array#unshift" do
+  it "prepends object to the original array" do
+    a = [1, 2, 3]
+    a.unshift("a").should equal(a)
+    a.should == ['a', 1, 2, 3]
+    a.unshift().should equal(a)
+    a.should == ['a', 1, 2, 3]
+    a.unshift(5, 4, 3)
+    a.should == [5, 4, 3, 'a', 1, 2, 3]
+
+    # shift all but one element
+    a = [1, 2]
+    a.shift
+    a.unshift(3, 4)
+    a.should == [3, 4, 2]
+
+    # now shift all elements
+    a.shift
+    a.shift
+    a.shift
+    a.unshift(3, 4)
+    a.should == [3, 4]
+  end
+
+  it "quietly ignores unshifting nothing" do
+    [].unshift().should == []
+    [].unshift(*[]).should == []
+  end
+
+  it "properly handles recursive arrays" do
+    empty = ArraySpecs.empty_recursive_array
+    empty.unshift(:new).should == [:new, empty]
+
+    array = ArraySpecs.recursive_array
+    array.unshift(:new)
+    array[0..5].should == [:new, 1, 'two', 3.0, array, array]
+  end
+
+  it "raises a RuntimeError on a frozen array when the array is modified" do
+    lambda { ArraySpecs.frozen_array.unshift(1) }.should raise_error(RuntimeError)
+  end
+
+  # see [ruby-core:23666]
+  it "raises a RuntimeError on a frozen array when the array would not be modified" do
+    lambda { ArraySpecs.frozen_array.unshift    }.should raise_error(RuntimeError)
+  end
+end