Add spec for File::Spec.pipe?

spec/ruby/core/file/stat/pipe_spec.rb

@@ -7,5 +7,26 @@
 end
 
 describe "File::Stat#pipe?" do
-  it "needs to be reviewed for spec completeness"
+  it "returns false if the file is not a pipe" do
+    filename = tmp("i_exist")
+    touch(filename)
+
+    st = File.stat(filename)
+    st.pipe?.should == false
+
+    rm_r filename
+  end
+
+  platform_is_not :windows do
+    it "returns true if the file is a pipe" do
+      filename = tmp("i_am_a_pipe")
+      system "mkfifo #{filename}"
+
+      st = File.stat(filename)
+      st.pipe?.should == true
+
+      rm_r filename
+    end
+  end
+
 end