1 files changed, 16 insertions, 0 deletions
diff --git a/spec/ruby/core/kernel/sprintf_spec.rb b/spec/ruby/core/kernel/sprintf_spec.rb
index 7adf71be76..9ef7f86f16 100644
--- a/spec/ruby/core/kernel/sprintf_spec.rb
+++ b/spec/ruby/core/kernel/sprintf_spec.rb
@@ -3,6 +3,14 @@ require_relative 'fixtures/classes'
 require_relative 'shared/sprintf'
 require_relative 'shared/sprintf_encoding'
 
+describe :kernel_sprintf_to_str, shared: true do
+  it "calls #to_str to convert the format object to a String" do
+    obj = mock('format string')
+    obj.should_receive(:to_str).and_return("to_str: %i")
+    @method.call(obj, 42).should == "to_str: 42"
+  end
+end
+
 describe "Kernel#sprintf" do
   it_behaves_like :kernel_sprintf, -> format, *args {
     sprintf(format, *args)
@@ -11,6 +19,10 @@ describe "Kernel#sprintf" do
   it_behaves_like :kernel_sprintf_encoding, -> format, *args {
     sprintf(format, *args)
   }
+
+  it_behaves_like :kernel_sprintf_to_str, -> format, *args {
+    sprintf(format, *args)
+  }
 end
 
 describe "Kernel.sprintf" do
@@ -21,4 +33,8 @@ describe "Kernel.sprintf" do
   it_behaves_like :kernel_sprintf_encoding, -> format, *args {
     Kernel.sprintf(format, *args)
   }
+
+  it_behaves_like :kernel_sprintf_to_str, -> format, *args {
+    Kernel.sprintf(format, *args)
+  }
 end