Improve IO::Buffer specs

Author: eregon

core/io/buffer/for_spec.rb

@@ -66,6 +66,7 @@
           buffer.get_string.should == @string.b
 
           buffer.should_not.readonly?
+          buffer.should_not.locked?
 
           buffer.set_string("ghost shell")
           @string.should == "ghost shellg"

core/io/buffer/map_spec.rb

@@ -73,7 +73,7 @@ def open_big_file_fixture
     @buffer.should.valid?
   end
 
-  platform_is_not :windows, :openbsd do
+  guard -> { Process.respond_to?(:fork) } do
     it "is shareable across processes" do
       file_name = tmp("shared_buffer")
       @file = File.open(file_name, "w+")
@@ -312,7 +312,7 @@ def open_big_file_fixture
         @file.read.should == "abcâdef\n".b
       end
 
-      platform_is_not :windows do
+      guard -> { Process.respond_to?(:fork) } do
         it "is not shared across processes" do
           file_name = tmp("shared_buffer")
           @file = File.open(file_name, "w+")

core/io/buffer/transfer_spec.rb

@@ -91,8 +91,9 @@
   context "with a slice of a buffer" do
     it "transfers source to a new slice, not touching the buffer" do
       @buffer = IO::Buffer.new(4)
-      slice = @buffer.slice(0, 2)
       @buffer.set_string("test")
+      slice = @buffer.slice(0, 2)
+      slice.get_string.should == "te"
 
       new_slice = slice.transfer
       slice.null?.should == true