1 files changed, 31 insertions, 10 deletions
diff --git a/spec/ruby/library/stringio/printf_spec.rb b/spec/ruby/library/stringio/printf_spec.rb
index 3978896621..ca82e84757 100644
--- a/spec/ruby/library/stringio/printf_spec.rb
+++ b/spec/ruby/library/stringio/printf_spec.rb
@@ -4,7 +4,7 @@ require_relative '../../core/kernel/shared/sprintf'
 
 describe "StringIO#printf" do
   before :each do
-    @io = StringIO.new('example')
+    @io = StringIO.new()
   end
 
   it "returns nil" do
@@ -12,9 +12,9 @@ describe "StringIO#printf" do
   end
 
   it "pads self with \\000 when the current position is after the end" do
-    @io.pos = 10
+    @io.pos = 3
     @io.printf("%d", 123)
-    @io.string.should == "example\000\000\000123"
+    @io.string.should == "\000\000\000123"
   end
 
   it "performs format conversion" do
@@ -31,17 +31,38 @@ describe "StringIO#printf" do
   end
 
   describe "formatting" do
-    it_behaves_like :kernel_sprintf, -> (format, *args) {
-      io = StringIO.new
+    it_behaves_like :kernel_sprintf, -> format, *args {
+      io = StringIO.new(+"")
       io.printf(format, *args)
       io.string
     }
   end
 end
 
+describe "StringIO#printf when in read-write mode" do
+  before :each do
+    @io = StringIO.new(+"example", "r+")
+  end
+
+  it "starts from the beginning" do
+    @io.printf("%s", "abcdefghijk")
+    @io.string.should == "abcdefghijk"
+  end
+
+  it "does not truncate existing string" do
+    @io.printf("%s", "abc")
+    @io.string.should == "abcmple"
+  end
+
+  it "correctly updates self's position" do
+    @io.printf("%s", "abc")
+    @io.pos.should eql(3)
+  end
+end
+
 describe "StringIO#printf when in append mode" do
   before :each do
-    @io = StringIO.new("example", "a")
+    @io = StringIO.new(+"example", "a")
   end
 
   it "appends the passed argument to the end of self" do
@@ -60,11 +81,11 @@ end
 
 describe "StringIO#printf when self is not writable" do
   it "raises an IOError" do
-    io = StringIO.new("test", "r")
-    lambda { io.printf("test") }.should raise_error(IOError)
+    io = StringIO.new(+"test", "r")
+    -> { io.printf("test") }.should raise_error(IOError)
 
-    io = StringIO.new("test")
+    io = StringIO.new(+"test")
     io.close_write
-    lambda { io.printf("test") }.should raise_error(IOError)
+    -> { io.printf("test") }.should raise_error(IOError)
   end
 end