Add explicit mutator for op_asgn

lib/mutant.rb

@@ -69,6 +69,7 @@ require 'mutant/mutator/node/named_value/access'
 require 'mutant/mutator/node/named_value/constant_assignment'
 require 'mutant/mutator/node/named_value/variable_assignment'
 require 'mutant/mutator/node/noop'
+require 'mutant/mutator/node/op_asgn'
 require 'mutant/mutator/node/while'
 require 'mutant/mutator/node/super'
 require 'mutant/mutator/node/zsuper'

lib/mutant/mutator/node/generic.rb

@@ -12,7 +12,7 @@ module Mutant
         handle(
           :next, :break, :ensure,
           :dsym, :yield, :rescue, :redo, :defined?,
-          :blockarg, :op_asgn, :and_asgn,
+          :blockarg, :and_asgn,
           :regopt, :restarg, :resbody, :retry, :arg_expr,
           :kwrestarg, :kwoptarg, :kwarg, :undef, :module, :empty,
           :alias, :for, :xstr, :back_ref, :class,

lib/mutant/mutator/node/op_asgn.rb

@@ -0,0 +1,30 @@
+# encoding: utf-8
+
+module Mutant
+  class Mutator
+    class Node
+
+      # OpAsgn mutator
+      class OpAsgn < Generic
+
+        handle(:op_asgn)
+
+        children :left, :right
+
+      private
+
+        # Emit mutations
+        #
+        # @return [undefined]
+        #
+        # @api private
+        #
+        def dispatch
+          super
+          emit_nil
+        end
+
+      end # OpAsgn
+    end # Node
+  end # Mutator
+end # Mutant

spec/unit/mutant/mutator/node/op_assgn/mutation_spec.rb

@@ -5,7 +5,7 @@ require 'spec_helper'
 describe Mutant::Mutator::Node::Generic, 'op_asgn' do
   let(:random_fixnum) { 5 }
 
-  let(:source)  { '@a.b += 1' }
+  let(:source) { '@a.b += 1' }
 
   let(:mutations) do
     mutations = []
@@ -16,6 +16,7 @@ describe Mutant::Mutator::Node::Generic, 'op_asgn' do
     mutations << '@a += 1'
     mutations << '@a.b += 5'
     mutations << 'nil.b += 1'
+    mutations << 'nil'
   end
 
   before do