13 files changed, 30 insertions, 25 deletions
diff --git a/spec/ruby/core/string/shared/chars.rb b/spec/ruby/core/string/shared/chars.rb
index e9fdf89fd6..c730643cf4 100644
--- a/spec/ruby/core/string/shared/chars.rb
+++ b/spec/ruby/core/string/shared/chars.rb
@@ -21,12 +21,12 @@ describe :string_chars, shared: true do
   end
 
   it "returns characters in the same encoding as self" do
-    "&%".force_encoding('Shift_JIS').send(@method).to_a.all? {|c| c.encoding.name.should == 'Shift_JIS'}
+    "&%".dup.force_encoding('Shift_JIS').send(@method).to_a.all? {|c| c.encoding.name.should == 'Shift_JIS'}
     "&%".encode('BINARY').send(@method).to_a.all? {|c| c.encoding.should == Encoding::BINARY }
   end
 
   it "works with multibyte characters" do
-    s = "\u{8987}".force_encoding("UTF-8")
+    s = "\u{8987}".dup.force_encoding("UTF-8")
     s.bytesize.should == 3
     s.send(@method).to_a.should == [s]
   end
@@ -39,14 +39,14 @@ describe :string_chars, shared: true do
   end
 
   it "returns a different character if the String is transcoded" do
-    s = "\u{20AC}".force_encoding('UTF-8')
-    s.encode('UTF-8').send(@method).to_a.should == ["\u{20AC}".force_encoding('UTF-8')]
+    s = "\u{20AC}".dup.force_encoding('UTF-8')
+    s.encode('UTF-8').send(@method).to_a.should == ["\u{20AC}".dup.force_encoding('UTF-8')]
     s.encode('iso-8859-15').send(@method).to_a.should == [[0xA4].pack('C').force_encoding('iso-8859-15')]
-    s.encode('iso-8859-15').encode('UTF-8').send(@method).to_a.should == ["\u{20AC}".force_encoding('UTF-8')]
+    s.encode('iso-8859-15').encode('UTF-8').send(@method).to_a.should == ["\u{20AC}".dup.force_encoding('UTF-8')]
   end
 
   it "uses the String's encoding to determine what characters it contains" do
-    s = "\u{24B62}"
+    s = +"\u{24B62}"
 
     s.force_encoding('UTF-8').send(@method).to_a.should == [
       s.force_encoding('UTF-8')
diff --git a/spec/ruby/core/string/shared/codepoints.rb b/spec/ruby/core/string/shared/codepoints.rb
index 0b2e078e0a..f71263054a 100644
--- a/spec/ruby/core/string/shared/codepoints.rb
+++ b/spec/ruby/core/string/shared/codepoints.rb
@@ -7,7 +7,7 @@ describe :string_codepoints, shared: true do
   end
 
   it "raises an ArgumentError when self has an invalid encoding and a method is called on the returned Enumerator" do
-    s = "\xDF".force_encoding(Encoding::UTF_8)
+    s = "\xDF".dup.force_encoding(Encoding::UTF_8)
     s.valid_encoding?.should be_false
     -> { s.send(@method).to_a }.should raise_error(ArgumentError)
   end
@@ -21,7 +21,7 @@ describe :string_codepoints, shared: true do
   end
 
   it "raises an ArgumentError if self's encoding is invalid and a block is given" do
-    s = "\xDF".force_encoding(Encoding::UTF_8)
+    s = "\xDF".dup.force_encoding(Encoding::UTF_8)
     s.valid_encoding?.should be_false
     -> { s.send(@method) { } }.should raise_error(ArgumentError)
   end
@@ -49,7 +49,7 @@ describe :string_codepoints, shared: true do
 
   it "round-trips to the original String using Integer#chr" do
     s = "\u{13}\u{7711}\u{1010}"
-    s2 = ""
+    s2 = +""
     s.send(@method) {|n| s2 << n.chr(Encoding::UTF_8)}
     s.should == s2
   end
diff --git a/spec/ruby/core/string/shared/concat.rb b/spec/ruby/core/string/shared/concat.rb
index ee5ef2a98f..dded9a69e7 100644
--- a/spec/ruby/core/string/shared/concat.rb
+++ b/spec/ruby/core/string/shared/concat.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: false
 describe :string_concat, shared: true do
   it "concatenates the given argument to self and returns self" do
     str = 'hello '
diff --git a/spec/ruby/core/string/shared/dedup.rb b/spec/ruby/core/string/shared/dedup.rb
index 893fd1e360..97b5df6ed1 100644
--- a/spec/ruby/core/string/shared/dedup.rb
+++ b/spec/ruby/core/string/shared/dedup.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: false
 describe :string_dedup, shared: true do
   it 'returns self if the String is frozen' do
     input  = 'foo'.freeze
diff --git a/spec/ruby/core/string/shared/each_codepoint_without_block.rb b/spec/ruby/core/string/shared/each_codepoint_without_block.rb
index 92b7f76032..31b4c02c9c 100644
--- a/spec/ruby/core/string/shared/each_codepoint_without_block.rb
+++ b/spec/ruby/core/string/shared/each_codepoint_without_block.rb
@@ -6,7 +6,7 @@ describe :string_each_codepoint_without_block, shared: true do
     end
 
     it "returns an Enumerator even when self has an invalid encoding" do
-      s = "\xDF".force_encoding(Encoding::UTF_8)
+      s = "\xDF".dup.force_encoding(Encoding::UTF_8)
       s.valid_encoding?.should be_false
       s.send(@method).should be_an_instance_of(Enumerator)
     end
@@ -23,7 +23,7 @@ describe :string_each_codepoint_without_block, shared: true do
         end
 
         it "should return the size of the string even when the string has an invalid encoding" do
-          s = "\xDF".force_encoding(Encoding::UTF_8)
+          s = "\xDF".dup.force_encoding(Encoding::UTF_8)
           s.valid_encoding?.should be_false
           s.send(@method).size.should == 1
         end
diff --git a/spec/ruby/core/string/shared/each_line.rb b/spec/ruby/core/string/shared/each_line.rb
index a14b4d7779..231a6d9d4f 100644
--- a/spec/ruby/core/string/shared/each_line.rb
+++ b/spec/ruby/core/string/shared/each_line.rb
@@ -106,7 +106,7 @@ describe :string_each_line, shared: true do
   end
 
   it "does not care if the string is modified while substituting" do
-    str = "hello\nworld."
+    str = +"hello\nworld."
     out = []
     str.send(@method){|x| out << x; str[-1] = '!' }.should == "hello\nworld!"
     out.should == ["hello\n", "world."]
diff --git a/spec/ruby/core/string/shared/encode.rb b/spec/ruby/core/string/shared/encode.rb
index a73de5b943..3776e0d709 100644
--- a/spec/ruby/core/string/shared/encode.rb
+++ b/spec/ruby/core/string/shared/encode.rb
@@ -1,4 +1,5 @@
 # -*- encoding: utf-8 -*-
+# frozen_string_literal: false
 describe :string_encode, shared: true do
   describe "when passed no options" do
     it "transcodes to Encoding.default_internal when set" do
diff --git a/spec/ruby/core/string/shared/eql.rb b/spec/ruby/core/string/shared/eql.rb
index 6f268c929c..845b0a3e15 100644
--- a/spec/ruby/core/string/shared/eql.rb
+++ b/spec/ruby/core/string/shared/eql.rb
@@ -13,15 +13,15 @@ describe :string_eql_value, shared: true do
   end
 
   it "ignores encoding difference of compatible string" do
-    "hello".force_encoding("utf-8").send(@method, "hello".force_encoding("iso-8859-1")).should be_true
+    "hello".dup.force_encoding("utf-8").send(@method, "hello".dup.force_encoding("iso-8859-1")).should be_true
   end
 
   it "considers encoding difference of incompatible string" do
-    "\xff".force_encoding("utf-8").send(@method, "\xff".force_encoding("iso-8859-1")).should be_false
+    "\xff".dup.force_encoding("utf-8").send(@method, "\xff".dup.force_encoding("iso-8859-1")).should be_false
   end
 
   it "considers encoding compatibility" do
-    "abcd".force_encoding("utf-8").send(@method, "abcd".force_encoding("utf-32le")).should be_false
+    "abcd".dup.force_encoding("utf-8").send(@method, "abcd".dup.force_encoding("utf-32le")).should be_false
   end
 
   it "ignores subclass differences" do
@@ -33,6 +33,6 @@ describe :string_eql_value, shared: true do
   end
 
   it "returns true when comparing 2 empty strings but one is not ASCII-compatible" do
-    "".send(@method, "".force_encoding('iso-2022-jp')).should == true
+    "".send(@method, "".dup.force_encoding('iso-2022-jp')).should == true
   end
 end
diff --git a/spec/ruby/core/string/shared/length.rb b/spec/ruby/core/string/shared/length.rb
index 94e5ec135b..ae572ba755 100644
--- a/spec/ruby/core/string/shared/length.rb
+++ b/spec/ruby/core/string/shared/length.rb
@@ -18,7 +18,7 @@ describe :string_length, shared: true do
   end
 
   it "returns the length of the new self after encoding is changed" do
-    str = 'こにちわ'
+    str = +'こにちわ'
     str.send(@method)
 
     str.force_encoding('BINARY').send(@method).should == 12
@@ -44,12 +44,12 @@ describe :string_length, shared: true do
   end
 
   it "adds 1 (and not 2) for a incomplete surrogate in UTF-16" do
-    "\x00\xd8".force_encoding("UTF-16LE").send(@method).should == 1
-    "\xd8\x00".force_encoding("UTF-16BE").send(@method).should == 1
+    "\x00\xd8".dup.force_encoding("UTF-16LE").send(@method).should == 1
+    "\xd8\x00".dup.force_encoding("UTF-16BE").send(@method).should == 1
   end
 
   it "adds 1 for a broken sequence in UTF-32" do
-    "\x04\x03\x02\x01".force_encoding("UTF-32LE").send(@method).should == 1
-    "\x01\x02\x03\x04".force_encoding("UTF-32BE").send(@method).should == 1
+    "\x04\x03\x02\x01".dup.force_encoding("UTF-32LE").send(@method).should == 1
+    "\x01\x02\x03\x04".dup.force_encoding("UTF-32BE").send(@method).should == 1
   end
 end
diff --git a/spec/ruby/core/string/shared/replace.rb b/spec/ruby/core/string/shared/replace.rb
index a5108d9e7c..24dac0eb27 100644
--- a/spec/ruby/core/string/shared/replace.rb
+++ b/spec/ruby/core/string/shared/replace.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: false
 describe :string_replace, shared: true do
   it "returns self" do
     a = "a"
diff --git a/spec/ruby/core/string/shared/slice.rb b/spec/ruby/core/string/shared/slice.rb
index 3ef4bc50d7..2f69b9ddce 100644
--- a/spec/ruby/core/string/shared/slice.rb
+++ b/spec/ruby/core/string/shared/slice.rb
@@ -84,8 +84,8 @@ describe :string_slice_index_length, shared: true do
     s = "hello there"
     s.send(@method, 1, 9).encoding.should == s.encoding
 
-    a = "hello".force_encoding("binary")
-    b = " there".force_encoding("ISO-8859-1")
+    a = "hello".dup.force_encoding("binary")
+    b = " there".dup.force_encoding("ISO-8859-1")
     c = (a + b).force_encoding(Encoding::US_ASCII)
 
     c.send(@method, 0, 5).encoding.should == Encoding::US_ASCII
diff --git a/spec/ruby/core/string/shared/succ.rb b/spec/ruby/core/string/shared/succ.rb
index 24a729ce26..b69a394875 100644
--- a/spec/ruby/core/string/shared/succ.rb
+++ b/spec/ruby/core/string/shared/succ.rb
@@ -73,6 +73,7 @@ end
 describe :string_succ_bang, shared: true do
   it "is equivalent to succ, but modifies self in place (still returns self)" do
     ["", "abcd", "THX1138"].each do |s|
+      s = +s
       r = s.dup.send(@method)
       s.send(@method).should equal(s)
       s.should == r
diff --git a/spec/ruby/core/string/shared/to_sym.rb b/spec/ruby/core/string/shared/to_sym.rb
index 52d8314211..833eae100e 100644
--- a/spec/ruby/core/string/shared/to_sym.rb
+++ b/spec/ruby/core/string/shared/to_sym.rb
@@ -56,9 +56,9 @@ describe :string_to_sym, shared: true do
   it "ignores existing symbols with different encoding" do
     source = "fée"
 
-    iso_symbol = source.force_encoding(Encoding::ISO_8859_1).send(@method)
+    iso_symbol = source.dup.force_encoding(Encoding::ISO_8859_1).send(@method)
     iso_symbol.encoding.should == Encoding::ISO_8859_1
-    binary_symbol = source.force_encoding(Encoding::BINARY).send(@method)
+    binary_symbol = source.dup.force_encoding(Encoding::BINARY).send(@method)
     binary_symbol.encoding.should == Encoding::BINARY
   end