Test command mutating eval_string instead of Ruby doing it

It probably isn't actually important to support Ruby mutating
eval_string.

spec/helpers/repl_tester.rb

@@ -9,9 +9,9 @@ class ReplTester
     end
   end
 
-  def self.start(&block)
+  def self.start(options = {}, &block)
     redirect_pry_io Input.new, StringIO.new do
-      instance = new
+      instance = new(options)
       instance.instance_eval(&block)
       instance.ensure_exit
     end
@@ -19,8 +19,8 @@ class ReplTester
 
   attr_accessor :pry, :repl, :fiber
 
-  def initialize
-    @pry   = Pry.new
+  def initialize(options = {})
+    @pry   = Pry.new(options)
     @repl  = Pry::REPL.new(@pry)
 
     @fiber = Fiber.new do

spec/pry_repl_spec.rb

@@ -47,10 +47,23 @@ describe "The REPL" do
       end
     end
 
-    it "should immediately evaluate if eval_string is complete" do
-      ReplTester.start do
-        input  '_pry_.eval_string = "10"'
-        output '=> 10'
+    it "should immediately evaluate eval_string after cmd if complete" do
+      set = Pry::CommandSet.new do
+        import Pry::Commands
+
+        command 'hello!' do
+          eval_string.replace('"hello"')
+        end
+      end
+
+      ReplTester.start(:commands => set) do
+        input  'def x'
+        output ''
+        prompt /\* $/
+
+        input  'hello!'
+        output '=> "hello"'
+        prompt /> $/
       end
     end
   end