1 files changed, 8 insertions, 7 deletions
diff --git a/spec/ruby/core/encoding/converter/convert_spec.rb b/spec/ruby/core/encoding/converter/convert_spec.rb
index 95a9e0b758..7f249d90a3 100644
--- a/spec/ruby/core/encoding/converter/convert_spec.rb
+++ b/spec/ruby/core/encoding/converter/convert_spec.rb
@@ -1,4 +1,5 @@
 # -*- encoding: binary -*-
+# frozen_string_literal: true
 require_relative '../../../spec_helper'
 
 describe "Encoding::Converter#convert" do
@@ -9,31 +10,31 @@ describe "Encoding::Converter#convert" do
 
   it "sets the encoding of the result to the target encoding" do
     ec = Encoding::Converter.new('ascii', 'utf-8')
-    str = 'glark'.force_encoding('ascii')
+    str = 'glark'.dup.force_encoding('ascii')
     ec.convert(str).encoding.should == Encoding::UTF_8
   end
 
   it "transcodes the given String to the target encoding" do
     ec = Encoding::Converter.new("utf-8", "euc-jp")
-    ec.convert("\u3042".force_encoding('UTF-8')).should == \
-      "\xA4\xA2".force_encoding('EUC-JP')
+    ec.convert("\u3042".dup.force_encoding('UTF-8')).should == \
+      "\xA4\xA2".dup.force_encoding('EUC-JP')
   end
 
   it "allows Strings of different encodings to the source encoding" do
     ec = Encoding::Converter.new('ascii', 'utf-8')
-    str = 'glark'.force_encoding('SJIS')
+    str = 'glark'.dup.force_encoding('SJIS')
     ec.convert(str).encoding.should == Encoding::UTF_8
   end
 
   it "reuses the given encoding pair if called multiple times" do
     ec = Encoding::Converter.new('ascii', 'SJIS')
-    ec.convert('a'.force_encoding('ASCII')).should == 'a'.force_encoding('SJIS')
-    ec.convert('b'.force_encoding('ASCII')).should == 'b'.force_encoding('SJIS')
+    ec.convert('a'.dup.force_encoding('ASCII')).should == 'a'.dup.force_encoding('SJIS')
+    ec.convert('b'.dup.force_encoding('ASCII')).should == 'b'.dup.force_encoding('SJIS')
   end
 
   it "raises UndefinedConversionError if the String contains characters invalid for the target encoding" do
     ec = Encoding::Converter.new('UTF-8', Encoding.find('macCyrillic'))
-    -> { ec.convert("\u{6543}".force_encoding('UTF-8')) }.should \
+    -> { ec.convert("\u{6543}".dup.force_encoding('UTF-8')) }.should \
       raise_error(Encoding::UndefinedConversionError)
   end