Fix Mutant::Expression#inspect to be more usable

config/flay.yml

@@ -1,3 +1,3 @@
 ---
 threshold: 18
-total_score: 1040
+total_score: 1043

lib/mutant/expression.rb

@@ -13,6 +13,8 @@ module Mutant
       *AST::Types::OPERATOR_METHODS.map(&:to_s)
     ).freeze
 
+    INSPECT_FORMAT = '<Mutant::Expression: %s>'.freeze
+
     SCOPE_PATTERN = /#{SCOPE_NAME_PATTERN}(?:#{SCOPE_OPERATOR}#{SCOPE_NAME_PATTERN})*/.freeze
 
     REGISTRY = {}
@@ -32,8 +34,17 @@ module Mutant
     def initialize(*)
       super
       @syntax = match.to_s
+      @inspect = format(INSPECT_FORMAT, syntax)
     end
 
+    # Return inspection
+    #
+    # @return [String]
+    #
+    # @api private
+    #
+    attr_reader :inspect
+
     # Return syntax
     #
     # @return [String]

spec/unit/mutant/expression_spec.rb

@@ -35,6 +35,14 @@ describe Mutant::Expression do
     end
   end
 
+  describe '#inspect' do
+    let(:object) { described_class.parse('Foo') }
+    subject { object.inspect }
+
+    it { should eql('<Mutant::Expression: Foo>') }
+    it_should_behave_like 'an idempotent method'
+  end
+
   describe '.parse' do
     subject { object.parse(input) }