Change to always insert mutations with frozen string literals

Changelog.md

@@ -1,3 +1,7 @@
+# v0.8.24 2018-12-xx
+
+* Change to always insert mutations with frozen string literals
+
 # v0.8.23 2018-12-23
 
 * Improved isolation error reporting

lib/mutant/loader.rb

@@ -5,6 +5,10 @@ module Mutant
   class Loader
     include Anima.new(:binding, :kernel, :source, :subject)
 
+    FROZEN_STRING_FORMAT = "# frozen_string_literal: true\n%s"
+
+    private_constant(*constants(false))
+
     # Call loader
     #
     # @return [self]
@@ -19,7 +23,7 @@ module Mutant
     # @return [undefined]
     def call
       kernel.eval(
-        source,
+        FROZEN_STRING_FORMAT % source,
         binding,
         subject.source_path.to_s,
         subject.source_line

spec/unit/mutant/loader_spec.rb

@@ -29,7 +29,7 @@ RSpec.describe Mutant::Loader, '.call' do
   it 'performs expected kernel interaction' do
     expect(kernel).to receive(:eval)
       .with(
-        source,
+        "# frozen_string_literal: true\n#[InstanceDouble(String) (anonymous)]",
         binding,
         path_str,
         line