1 files changed, 10 insertions, 0 deletions
diff --git a/spec/ruby/library/stringio/printf_spec.rb b/spec/ruby/library/stringio/printf_spec.rb
index 5f811547bc..a2094bf52d 100644
--- a/spec/ruby/library/stringio/printf_spec.rb
+++ b/spec/ruby/library/stringio/printf_spec.rb
@@ -1,5 +1,6 @@
 require File.expand_path('../../../spec_helper', __FILE__)
 require File.expand_path('../fixtures/classes', __FILE__)
+require File.expand_path('../../../core/kernel/shared/sprintf', __FILE__)
 
 describe "StringIO#printf" do
   before :each do
@@ -28,6 +29,14 @@ describe "StringIO#printf" do
     @io.printf("%d %04x", 123, 123)
     @io.pos.should eql(16)
   end
+
+  describe "formatting" do
+    it_behaves_like :kernel_sprintf, -> (format, *args) {
+      io = StringIO.new
+      io.printf(format, *args)
+      io.string
+    }
+  end
 end
 
 describe "StringIO#printf when in append mode" do
@@ -59,3 +68,4 @@ describe "StringIO#printf when self is not writable" do
     lambda { io.printf("test") }.should raise_error(IOError)
   end
 end
+