Add message matchers for exception specs in IO#pwrite

core/io/pwrite_spec.rb

@@ -29,9 +29,9 @@
     end
 
     it "calls #to_s on the object to be written" do
-      data = mock("to_s")
-      data.should_receive(:to_s).and_return("foo")
-      @file.pwrite(data, 0)
+      object = mock("to_s")
+      object.should_receive(:to_s).and_return("foo")
+      @file.pwrite(object, 0)
       @file.pread(3, 0).should == "foo"
     end
 
@@ -44,17 +44,17 @@
 
     it "raises IOError when file is not open in write mode" do
       File.open(@fname, "r") do |file|
-        -> { file.pwrite("foo", 1) }.should raise_error(IOError)
+        -> { file.pwrite("foo", 1) }.should raise_error(IOError, "not opened for writing")
       end
     end
 
     it "raises IOError when file is closed" do
       file = File.open(@fname, "w+")
       file.close
-      -> { file.pwrite("foo", 1) }.should raise_error(IOError)
+      -> { file.pwrite("foo", 1) }.should raise_error(IOError, "closed stream")
     end
 
-    it "raises a NoMethodError if #to_s cannot be called on the object to be written" do
+    it "raises a NoMethodError if object does not respond to #to_s" do
       -> {
         @file.pwrite(BasicObject.new, 0)
       }.should raise_error(NoMethodError, /undefined method `to_s'/)