1 files changed, 40 insertions, 4 deletions
diff --git a/spec/ruby/core/kernel/printf_spec.rb b/spec/ruby/core/kernel/printf_spec.rb
index b4c68fa449..50939b3794 100644
--- a/spec/ruby/core/kernel/printf_spec.rb
+++ b/spec/ruby/core/kernel/printf_spec.rb
@@ -1,14 +1,14 @@
-require File.expand_path('../../../spec_helper', __FILE__)
-require File.expand_path('../fixtures/classes', __FILE__)
+require_relative '../../spec_helper'
+require_relative 'fixtures/classes'
+require_relative 'shared/sprintf'
 
 describe "Kernel#printf" do
   it "is a private method" do
-    Kernel.should have_private_instance_method(:printf)
+    Kernel.private_instance_methods(false).should.include?(:printf)
   end
 end
 
 describe "Kernel.printf" do
-
   before :each do
     @stdout = $stdout
     @name = tmp("kernel_puts.txt")
@@ -31,4 +31,40 @@ describe "Kernel.printf" do
     object.should_receive(:write).with("string")
     Kernel.printf(object, "%s", "string")
   end
+
+  it "calls #to_str to convert the format object to a String" do
+    object = mock('format string')
+    object.should_receive(:to_str).and_return("to_str: %i")
+    $stdout.should_receive(:write).with("to_str: 42")
+    Kernel.printf($stdout, object, 42)
+  end
+end
+
+describe "Kernel.printf" do
+  describe "formatting" do
+    before :each do
+      require "stringio"
+    end
+
+    context "io is specified" do
+      it_behaves_like :kernel_sprintf, -> format, *args {
+        io = StringIO.new(+"")
+        Kernel.printf(io, format, *args)
+        io.string
+      }
+    end
+
+    context "io is not specified" do
+      it_behaves_like :kernel_sprintf, -> format, *args {
+        stdout = $stdout
+        begin
+          $stdout = io = StringIO.new(+"")
+          Kernel.printf(format, *args)
+          io.string
+        ensure
+          $stdout = stdout
+        end
+      }
+    end
+  end
 end