diff --git a/doc/jamis.rb b/doc/jamis.rb
index c7bc84ac5..531aa7573 100644
--- a/doc/jamis.rb
+++ b/doc/jamis.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module RDoc
 module Page
 
diff --git a/lib/rake.rb b/lib/rake.rb
index 07b03284b..0dfd05315 100644
--- a/lib/rake.rb
+++ b/lib/rake.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 #--
 # Copyright 2003-2010 by Jim Weirich (jim.weirich@gmail.com)
 #
diff --git a/lib/rake/application.rb b/lib/rake/application.rb
index e94f17290..ae594e098 100644
--- a/lib/rake/application.rb
+++ b/lib/rake/application.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require "optparse"
 
 require "rake/task_manager"
diff --git a/lib/rake/backtrace.rb b/lib/rake/backtrace.rb
index a89dd9f4d..31ff05450 100644
--- a/lib/rake/backtrace.rb
+++ b/lib/rake/backtrace.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
   module Backtrace # :nodoc: all
     SYS_KEYS  = RbConfig::CONFIG.keys.grep(/(?:[a-z]prefix|libdir)\z/)
diff --git a/lib/rake/clean.rb b/lib/rake/clean.rb
index f66353a0a..5af44015e 100644
--- a/lib/rake/clean.rb
+++ b/lib/rake/clean.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # The 'rake/clean' file defines two file lists (CLEAN and CLOBBER) and
 # two rake tasks (:clean and :clobber).
 #
diff --git a/lib/rake/cloneable.rb b/lib/rake/cloneable.rb
index d53645f2f..eddb77e2f 100644
--- a/lib/rake/cloneable.rb
+++ b/lib/rake/cloneable.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
   ##
   # Mixin for creating easily cloned objects.
diff --git a/lib/rake/cpu_counter.rb b/lib/rake/cpu_counter.rb
index 82a5eb8aa..f3bf6d630 100644
--- a/lib/rake/cpu_counter.rb
+++ b/lib/rake/cpu_counter.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
 
   # Based on a script at:
diff --git a/lib/rake/default_loader.rb b/lib/rake/default_loader.rb
index 6154408f4..d3b4650d3 100644
--- a/lib/rake/default_loader.rb
+++ b/lib/rake/default_loader.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
 
   # Default Rakefile loader used by +import+.
diff --git a/lib/rake/dsl_definition.rb b/lib/rake/dsl_definition.rb
index c52bd601f..3962c1679 100644
--- a/lib/rake/dsl_definition.rb
+++ b/lib/rake/dsl_definition.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # Rake DSL functions.
 require "rake/file_utils_ext"
 
diff --git a/lib/rake/early_time.rb b/lib/rake/early_time.rb
index abcb1872b..80cc6bfad 100644
--- a/lib/rake/early_time.rb
+++ b/lib/rake/early_time.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
 
   # EarlyTime is a fake timestamp that occurs _before_ any other time value.
diff --git a/lib/rake/ext/core.rb b/lib/rake/ext/core.rb
index 7575df15a..226f2125b 100644
--- a/lib/rake/ext/core.rb
+++ b/lib/rake/ext/core.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 class Module
   # Check for an existing method in the current class before extending.  If
   # the method already exists, then a warning is printed and the extension is
diff --git a/lib/rake/ext/string.rb b/lib/rake/ext/string.rb
index 37764c845..c70236ae9 100644
--- a/lib/rake/ext/string.rb
+++ b/lib/rake/ext/string.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require "rake/ext/core"
 
 class String
@@ -136,7 +137,7 @@ def pathmap_replace(patterns, &block)
     # This String extension comes from Rake
     def pathmap(spec=nil, &block)
       return self if spec.nil?
-      result = ""
+      result = "".dup
       spec.scan(/%\{[^}]*\}-?\d*[sdpfnxX%]|%-?\d+d|%.|[^%]+/) do |frag|
         case frag
         when "%f"
diff --git a/lib/rake/file_creation_task.rb b/lib/rake/file_creation_task.rb
index f3c5c78a1..2eb251bf1 100644
--- a/lib/rake/file_creation_task.rb
+++ b/lib/rake/file_creation_task.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require "rake/file_task"
 require "rake/early_time"
 
diff --git a/lib/rake/file_list.rb b/lib/rake/file_list.rb
index a30c6338c..748d668f1 100644
--- a/lib/rake/file_list.rb
+++ b/lib/rake/file_list.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require "rake/cloneable"
 require "rake/file_utils_ext"
 require "rake/ext/string"
diff --git a/lib/rake/file_task.rb b/lib/rake/file_task.rb
index cbb978e7f..474b7bd93 100644
--- a/lib/rake/file_task.rb
+++ b/lib/rake/file_task.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require "rake/task.rb"
 require "rake/early_time"
 
diff --git a/lib/rake/file_utils.rb b/lib/rake/file_utils.rb
index 3e56710e2..3439befab 100644
--- a/lib/rake/file_utils.rb
+++ b/lib/rake/file_utils.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require "rbconfig"
 require "fileutils"
 
diff --git a/lib/rake/file_utils_ext.rb b/lib/rake/file_utils_ext.rb
index e5930d4ab..bf558b749 100644
--- a/lib/rake/file_utils_ext.rb
+++ b/lib/rake/file_utils_ext.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require "rake/file_utils"
 
 module Rake
diff --git a/lib/rake/invocation_chain.rb b/lib/rake/invocation_chain.rb
index 540628957..44a995496 100644
--- a/lib/rake/invocation_chain.rb
+++ b/lib/rake/invocation_chain.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
 
   # InvocationChain tracks the chain of task invocations to detect
diff --git a/lib/rake/invocation_exception_mixin.rb b/lib/rake/invocation_exception_mixin.rb
index 84ff3353b..b0d307a48 100644
--- a/lib/rake/invocation_exception_mixin.rb
+++ b/lib/rake/invocation_exception_mixin.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
   module InvocationExceptionMixin
     # Return the invocation chain (list of Rake tasks) that were in
diff --git a/lib/rake/late_time.rb b/lib/rake/late_time.rb
index d1d9470ec..8fe024943 100644
--- a/lib/rake/late_time.rb
+++ b/lib/rake/late_time.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
   # LateTime is a fake timestamp that occurs _after_ any other time value.
   class LateTime
diff --git a/lib/rake/linked_list.rb b/lib/rake/linked_list.rb
index 54d0c1287..11fa46f0d 100644
--- a/lib/rake/linked_list.rb
+++ b/lib/rake/linked_list.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
 
   # Polylithic linked list structure used to implement several data
diff --git a/lib/rake/loaders/makefile.rb b/lib/rake/loaders/makefile.rb
index d0436bb79..46f4beaad 100644
--- a/lib/rake/loaders/makefile.rb
+++ b/lib/rake/loaders/makefile.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
 
   # Makefile loader to be used with the import file loader.  Use this to
diff --git a/lib/rake/multi_task.rb b/lib/rake/multi_task.rb
index 7118dc411..04c9f3109 100644
--- a/lib/rake/multi_task.rb
+++ b/lib/rake/multi_task.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
 
   # Same as a regular task, but the immediate prerequisites are done in
diff --git a/lib/rake/name_space.rb b/lib/rake/name_space.rb
index 0d7eb80b6..32f8139fc 100644
--- a/lib/rake/name_space.rb
+++ b/lib/rake/name_space.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 ##
 # The NameSpace class will lookup task names in the scope defined by a
 # +namespace+ command.
diff --git a/lib/rake/packagetask.rb b/lib/rake/packagetask.rb
index 034b8e9e8..f65affa6d 100644
--- a/lib/rake/packagetask.rb
+++ b/lib/rake/packagetask.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # Define a package task library to aid in the definition of
 # redistributable package files.
 
diff --git a/lib/rake/phony.rb b/lib/rake/phony.rb
index a172f9c60..8caa5de17 100644
--- a/lib/rake/phony.rb
+++ b/lib/rake/phony.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # Defines a :phony task that you can use as a dependency. This allows
 # file-based tasks to use non-file-based tasks as prerequisites
 # without forcing them to rebuild.
diff --git a/lib/rake/private_reader.rb b/lib/rake/private_reader.rb
index 162097857..2815ce643 100644
--- a/lib/rake/private_reader.rb
+++ b/lib/rake/private_reader.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
 
   # Include PrivateReader to use +private_reader+.
diff --git a/lib/rake/promise.rb b/lib/rake/promise.rb
index 37221e427..ecff4321e 100644
--- a/lib/rake/promise.rb
+++ b/lib/rake/promise.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
 
   # A Promise object represents a promise to do work (a chore) in the
diff --git a/lib/rake/pseudo_status.rb b/lib/rake/pseudo_status.rb
index 16e1903bd..8b3c98949 100644
--- a/lib/rake/pseudo_status.rb
+++ b/lib/rake/pseudo_status.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
 
   ##
diff --git a/lib/rake/rake_module.rb b/lib/rake/rake_module.rb
index 75feb1261..f5cfde58a 100644
--- a/lib/rake/rake_module.rb
+++ b/lib/rake/rake_module.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require "rake/application"
 
 module Rake
diff --git a/lib/rake/rake_test_loader.rb b/lib/rake/rake_test_loader.rb
index 98dcced06..ce3dd8eb6 100644
--- a/lib/rake/rake_test_loader.rb
+++ b/lib/rake/rake_test_loader.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require "rake"
 
 # Load the test files from the command line.
diff --git a/lib/rake/rule_recursion_overflow_error.rb b/lib/rake/rule_recursion_overflow_error.rb
index 39d44aac6..a51e77489 100644
--- a/lib/rake/rule_recursion_overflow_error.rb
+++ b/lib/rake/rule_recursion_overflow_error.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
 
   # Error indicating a recursion overflow error in task selection.
diff --git a/lib/rake/scope.rb b/lib/rake/scope.rb
index b432f5f29..27c05da89 100644
--- a/lib/rake/scope.rb
+++ b/lib/rake/scope.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
   class Scope < LinkedList # :nodoc: all
 
diff --git a/lib/rake/task.rb b/lib/rake/task.rb
index 23faf96e5..256571112 100644
--- a/lib/rake/task.rb
+++ b/lib/rake/task.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require "rake/invocation_exception_mixin"
 
 module Rake
@@ -320,7 +321,7 @@ def set_arg_names(args)
     # Return a string describing the internal state of a task.  Useful for
     # debugging.
     def investigation
-      result = "------------------------------\n"
+      result = "------------------------------\n".dup
       result << "Investigating #{name}\n"
       result << "class: #{self.class}\n"
       result <<  "task needed: #{needed?}\n"
diff --git a/lib/rake/task_argument_error.rb b/lib/rake/task_argument_error.rb
index 3e1dda64d..ef20076c6 100644
--- a/lib/rake/task_argument_error.rb
+++ b/lib/rake/task_argument_error.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
 
   # Error indicating an ill-formed task declaration.
diff --git a/lib/rake/task_arguments.rb b/lib/rake/task_arguments.rb
index c98057c8f..0d3001afd 100644
--- a/lib/rake/task_arguments.rb
+++ b/lib/rake/task_arguments.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
 
   ##
diff --git a/lib/rake/task_manager.rb b/lib/rake/task_manager.rb
index 971984ca5..8bc7d42a4 100644
--- a/lib/rake/task_manager.rb
+++ b/lib/rake/task_manager.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
 
   # The TaskManager module is a mixin for managing tasks.
diff --git a/lib/rake/tasklib.rb b/lib/rake/tasklib.rb
index 7bcda1789..5354b4f94 100644
--- a/lib/rake/tasklib.rb
+++ b/lib/rake/tasklib.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require "rake"
 
 module Rake
diff --git a/lib/rake/testtask.rb b/lib/rake/testtask.rb
index bb7f0ee8a..66e114762 100644
--- a/lib/rake/testtask.rb
+++ b/lib/rake/testtask.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require "rake"
 require "rake/tasklib"
 
diff --git a/lib/rake/thread_history_display.rb b/lib/rake/thread_history_display.rb
index 04273541e..412ea37be 100644
--- a/lib/rake/thread_history_display.rb
+++ b/lib/rake/thread_history_display.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require "rake/private_reader"
 
 module Rake
diff --git a/lib/rake/thread_pool.rb b/lib/rake/thread_pool.rb
index 1c2f5f50f..b01a5efe0 100644
--- a/lib/rake/thread_pool.rb
+++ b/lib/rake/thread_pool.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require "set"
 
 require "rake/promise"
diff --git a/lib/rake/trace_output.rb b/lib/rake/trace_output.rb
index c740b9e23..d713a0926 100644
--- a/lib/rake/trace_output.rb
+++ b/lib/rake/trace_output.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
   module TraceOutput # :nodoc: all
 
diff --git a/lib/rake/version.rb b/lib/rake/version.rb
index 1908ff855..a240aa5a4 100644
--- a/lib/rake/version.rb
+++ b/lib/rake/version.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Rake
   VERSION = "12.0.0"
 
diff --git a/lib/rake/win32.rb b/lib/rake/win32.rb
index 1fc02a5ae..6e6203181 100644
--- a/lib/rake/win32.rb
+++ b/lib/rake/win32.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require "rbconfig"
 
 module Rake
diff --git a/test/helper.rb b/test/helper.rb
index 532745319..a6e38cb18 100644
--- a/test/helper.rb
+++ b/test/helper.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 $:.unshift File.expand_path("../../lib", __FILE__)
 
 require 'coveralls'
diff --git a/test/support/file_creation.rb b/test/support/file_creation.rb
index facc57a03..a1313bc0e 100644
--- a/test/support/file_creation.rb
+++ b/test/support/file_creation.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module FileCreation
   OLDFILE = "old"
   NEWFILE = "new"
diff --git a/test/support/rakefile_definitions.rb b/test/support/rakefile_definitions.rb
index 9a19d43fc..5dacd3783 100644
--- a/test/support/rakefile_definitions.rb
+++ b/test/support/rakefile_definitions.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module RakefileDefinitions
   include FileUtils
 
diff --git a/test/support/ruby_runner.rb b/test/support/ruby_runner.rb
index 199f60dd6..160a57090 100644
--- a/test/support/ruby_runner.rb
+++ b/test/support/ruby_runner.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module RubyRunner
   include FileUtils
 
diff --git a/test/test_private_reader.rb b/test/test_private_reader.rb
index 56160f062..ef08c9d2c 100644
--- a/test/test_private_reader.rb
+++ b/test/test_private_reader.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "rake/private_reader"
 
diff --git a/test/test_rake.rb b/test/test_rake.rb
index dfbb7d232..2cdab492b 100644
--- a/test/test_rake.rb
+++ b/test/test_rake.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRake < Rake::TestCase
diff --git a/test/test_rake_application.rb b/test/test_rake_application.rb
index cd8feebbc..141dd576f 100644
--- a/test/test_rake_application.rb
+++ b/test/test_rake_application.rb
@@ -1,4 +1,4 @@
-#encoding: UTF-8
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakeApplication < Rake::TestCase
@@ -37,7 +37,7 @@ def test_display_exception_details
 
   def test_display_exception_details_bad_encoding
     begin
-      raise "El Niño is coming!".force_encoding("US-ASCII")
+      raise "El Niño is coming!".dup.force_encoding("US-ASCII")
     rescue => ex
     end
 
diff --git a/test/test_rake_application_options.rb b/test/test_rake_application_options.rb
index 149d8dcfd..b34c2f634 100644
--- a/test/test_rake_application_options.rb
+++ b/test/test_rake_application_options.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 TESTING_REQUIRE = []
diff --git a/test/test_rake_backtrace.rb b/test/test_rake_backtrace.rb
index ec727a292..d89817a11 100644
--- a/test/test_rake_backtrace.rb
+++ b/test/test_rake_backtrace.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "open3"
 
diff --git a/test/test_rake_clean.rb b/test/test_rake_clean.rb
index 5439a415f..612bd2546 100644
--- a/test/test_rake_clean.rb
+++ b/test/test_rake_clean.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "rake/clean"
 
diff --git a/test/test_rake_cpu_counter.rb b/test/test_rake_cpu_counter.rb
index aac16b2d7..3c3af15bf 100644
--- a/test/test_rake_cpu_counter.rb
+++ b/test/test_rake_cpu_counter.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakeCpuCounter < Rake::TestCase
diff --git a/test/test_rake_definitions.rb b/test/test_rake_definitions.rb
index 464cc6309..2dee13a34 100644
--- a/test/test_rake_definitions.rb
+++ b/test/test_rake_definitions.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "fileutils"
 
diff --git a/test/test_rake_directory_task.rb b/test/test_rake_directory_task.rb
index e42bd9c77..d5fd26f27 100644
--- a/test/test_rake_directory_task.rb
+++ b/test/test_rake_directory_task.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "fileutils"
 require "pathname"
diff --git a/test/test_rake_dsl.rb b/test/test_rake_dsl.rb
index 7f82c6afa..162961446 100644
--- a/test/test_rake_dsl.rb
+++ b/test/test_rake_dsl.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakeDsl < Rake::TestCase
diff --git a/test/test_rake_early_time.rb b/test/test_rake_early_time.rb
index 71ee3e157..dc0550b2a 100644
--- a/test/test_rake_early_time.rb
+++ b/test/test_rake_early_time.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakeEarlyTime < Rake::TestCase
diff --git a/test/test_rake_extension.rb b/test/test_rake_extension.rb
index 293ec1304..0627ef9b7 100644
--- a/test/test_rake_extension.rb
+++ b/test/test_rake_extension.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "stringio"
 
diff --git a/test/test_rake_file_creation_task.rb b/test/test_rake_file_creation_task.rb
index 35f843e9e..246f679c7 100644
--- a/test/test_rake_file_creation_task.rb
+++ b/test/test_rake_file_creation_task.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "fileutils"
 
diff --git a/test/test_rake_file_list.rb b/test/test_rake_file_list.rb
index 32ca7a8e3..7e5d1eed0 100644
--- a/test/test_rake_file_list.rb
+++ b/test/test_rake_file_list.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "pathname"
 
diff --git a/test/test_rake_file_list_path_map.rb b/test/test_rake_file_list_path_map.rb
index 28953a97a..71402cf36 100644
--- a/test/test_rake_file_list_path_map.rb
+++ b/test/test_rake_file_list_path_map.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakeFileListPathMap < Rake::TestCase
diff --git a/test/test_rake_file_task.rb b/test/test_rake_file_task.rb
index 24614dabe..774cbafd4 100644
--- a/test/test_rake_file_task.rb
+++ b/test/test_rake_file_task.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "fileutils"
 require "pathname"
diff --git a/test/test_rake_file_utils.rb b/test/test_rake_file_utils.rb
index 00ef76e41..bfdaf75bd 100644
--- a/test/test_rake_file_utils.rb
+++ b/test/test_rake_file_utils.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "fileutils"
 require "stringio"
diff --git a/test/test_rake_functional.rb b/test/test_rake_functional.rb
index 3496bc12d..daf832254 100644
--- a/test/test_rake_functional.rb
+++ b/test/test_rake_functional.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "fileutils"
 require "open3"
diff --git a/test/test_rake_invocation_chain.rb b/test/test_rake_invocation_chain.rb
index ba5f8724f..338180aaa 100644
--- a/test/test_rake_invocation_chain.rb
+++ b/test/test_rake_invocation_chain.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakeInvocationChain < Rake::TestCase
diff --git a/test/test_rake_late_time.rb b/test/test_rake_late_time.rb
index a88826da7..d07b441a0 100644
--- a/test/test_rake_late_time.rb
+++ b/test/test_rake_late_time.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakeLateTime < Rake::TestCase
diff --git a/test/test_rake_linked_list.rb b/test/test_rake_linked_list.rb
index a3c4d1972..d111575b2 100644
--- a/test/test_rake_linked_list.rb
+++ b/test/test_rake_linked_list.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestLinkedList < Rake::TestCase
diff --git a/test/test_rake_makefile_loader.rb b/test/test_rake_makefile_loader.rb
index bd70fd3b6..75713cd2f 100644
--- a/test/test_rake_makefile_loader.rb
+++ b/test/test_rake_makefile_loader.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "rake/loaders/makefile"
 
diff --git a/test/test_rake_multi_task.rb b/test/test_rake_multi_task.rb
index bab25b158..8a50c2980 100644
--- a/test/test_rake_multi_task.rb
+++ b/test/test_rake_multi_task.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "thread"
 
diff --git a/test/test_rake_name_space.rb b/test/test_rake_name_space.rb
index e043c07fa..e8d4d6b20 100644
--- a/test/test_rake_name_space.rb
+++ b/test/test_rake_name_space.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakeNameSpace < Rake::TestCase
diff --git a/test/test_rake_package_task.rb b/test/test_rake_package_task.rb
index 7bacb7a52..2634267ee 100644
--- a/test/test_rake_package_task.rb
+++ b/test/test_rake_package_task.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "rake/packagetask"
 
diff --git a/test/test_rake_path_map.rb b/test/test_rake_path_map.rb
index 040692930..92cf337cb 100644
--- a/test/test_rake_path_map.rb
+++ b/test/test_rake_path_map.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakePathMap < Rake::TestCase
diff --git a/test/test_rake_path_map_explode.rb b/test/test_rake_path_map_explode.rb
index 554a02266..3174d6ccc 100644
--- a/test/test_rake_path_map_explode.rb
+++ b/test/test_rake_path_map_explode.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakePathMapExplode < Rake::TestCase
diff --git a/test/test_rake_path_map_partial.rb b/test/test_rake_path_map_partial.rb
index 0adc24313..9daf44ca5 100644
--- a/test/test_rake_path_map_partial.rb
+++ b/test/test_rake_path_map_partial.rb
@@ -1,8 +1,9 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakePathMapPartial < Rake::TestCase
   def test_pathmap_partial
-    @path = "1/2/file"
+    @path = "1/2/file".dup
     def @path.call(n)
       pathmap_partial(n)
     end
diff --git a/test/test_rake_pseudo_status.rb b/test/test_rake_pseudo_status.rb
index d9fe42216..5a54bc200 100644
--- a/test/test_rake_pseudo_status.rb
+++ b/test/test_rake_pseudo_status.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakePseudoStatus < Rake::TestCase
diff --git a/test/test_rake_rake_test_loader.rb b/test/test_rake_rake_test_loader.rb
index 855606d4d..fa35c44aa 100644
--- a/test/test_rake_rake_test_loader.rb
+++ b/test/test_rake_rake_test_loader.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakeRakeTestLoader < Rake::TestCase
diff --git a/test/test_rake_reduce_compat.rb b/test/test_rake_reduce_compat.rb
index de81b474b..f3db9a79c 100644
--- a/test/test_rake_reduce_compat.rb
+++ b/test/test_rake_reduce_compat.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "open3"
 
diff --git a/test/test_rake_require.rb b/test/test_rake_require.rb
index c77344cc3..899aba5ca 100644
--- a/test/test_rake_require.rb
+++ b/test/test_rake_require.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakeRequire < Rake::TestCase
diff --git a/test/test_rake_rules.rb b/test/test_rake_rules.rb
index 35f0b45db..e71af3502 100644
--- a/test/test_rake_rules.rb
+++ b/test/test_rake_rules.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "fileutils"
 
diff --git a/test/test_rake_scope.rb b/test/test_rake_scope.rb
index 169c0d9f9..50bb1810b 100644
--- a/test/test_rake_scope.rb
+++ b/test/test_rake_scope.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakeScope < Rake::TestCase
diff --git a/test/test_rake_task.rb b/test/test_rake_task.rb
index 5f5a63e30..b2bbb6d95 100644
--- a/test/test_rake_task.rb
+++ b/test/test_rake_task.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "fileutils"
 
diff --git a/test/test_rake_task_argument_parsing.rb b/test/test_rake_task_argument_parsing.rb
index 4bc0ff0ae..e34126591 100644
--- a/test/test_rake_task_argument_parsing.rb
+++ b/test/test_rake_task_argument_parsing.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakeTaskArgumentParsing < Rake::TestCase
diff --git a/test/test_rake_task_arguments.rb b/test/test_rake_task_arguments.rb
index 383d4a172..2ae3652da 100644
--- a/test/test_rake_task_arguments.rb
+++ b/test/test_rake_task_arguments.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakeTaskArguments < Rake::TestCase
diff --git a/test/test_rake_task_manager.rb b/test/test_rake_task_manager.rb
index a611bd737..a9157ed81 100644
--- a/test/test_rake_task_manager.rb
+++ b/test/test_rake_task_manager.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakeTaskManager < Rake::TestCase
diff --git a/test/test_rake_task_manager_argument_resolution.rb b/test/test_rake_task_manager_argument_resolution.rb
index 6d292816d..c07be6f5e 100644
--- a/test/test_rake_task_manager_argument_resolution.rb
+++ b/test/test_rake_task_manager_argument_resolution.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakeTaskManagerArgumentResolution < Rake::TestCase
diff --git a/test/test_rake_task_with_arguments.rb b/test/test_rake_task_with_arguments.rb
index 5f71b6b1a..b7a9e03e7 100644
--- a/test/test_rake_task_with_arguments.rb
+++ b/test/test_rake_task_with_arguments.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakeTaskWithArguments < Rake::TestCase
diff --git a/test/test_rake_test_task.rb b/test/test_rake_test_task.rb
index 8e422f164..396e05924 100644
--- a/test/test_rake_test_task.rb
+++ b/test/test_rake_test_task.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "rake/testtask"
 
diff --git a/test/test_rake_thread_pool.rb b/test/test_rake_thread_pool.rb
index d365574ba..ceb8a5d1b 100644
--- a/test/test_rake_thread_pool.rb
+++ b/test/test_rake_thread_pool.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "rake/thread_pool"
 
diff --git a/test/test_rake_top_level_functions.rb b/test/test_rake_top_level_functions.rb
index a3bb2fbb8..f3675a096 100644
--- a/test/test_rake_top_level_functions.rb
+++ b/test/test_rake_top_level_functions.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakeTopLevelFunctions < Rake::TestCase
diff --git a/test/test_rake_win32.rb b/test/test_rake_win32.rb
index be95adb92..292af4715 100644
--- a/test/test_rake_win32.rb
+++ b/test/test_rake_win32.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 class TestRakeWin32 < Rake::TestCase
diff --git a/test/test_thread_history_display.rb b/test/test_thread_history_display.rb
index f3466cef7..8adb1940a 100644
--- a/test/test_thread_history_display.rb
+++ b/test/test_thread_history_display.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 
 require "rake/thread_history_display"
diff --git a/test/test_trace_output.rb b/test/test_trace_output.rb
index 18d2eee0f..34dab6162 100644
--- a/test/test_trace_output.rb
+++ b/test/test_trace_output.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require File.expand_path("../helper", __FILE__)
 require "stringio"
 
@@ -8,7 +9,7 @@ class PrintSpy
     attr_reader :result, :calls
 
     def initialize
-      @result = ""
+      @result = "".dup
       @calls = 0
     end