Add example for complex composition of predicate on matching

spec/unit/mutant/matcher/compiler_spec.rb

@@ -82,6 +82,33 @@ describe Mutant::Matcher::Compiler do
 
         it { should eql(expected_matcher) }
       end
+
+      context 'and subject and attribute filter' do
+        let(:attributes) do
+          {
+            match_expressions: [expression_a],
+            subject_ignores:   [expression_b],
+            subject_selects:   [[:code, 'foo']]
+          }
+        end
+
+        let(:expected_positive_matcher) { Mutant::Matcher::Chain.new([matcher_a]) }
+
+        let(:expected_predicate) do
+          Morpher::Evaluator::Predicate::Boolean::And.new([
+            Morpher::Evaluator::Predicate::Boolean::Or.new([
+              Morpher.compile(s(:eql, s(:attribute, :code), s(:static, 'foo')))
+            ]),
+            Morpher::Evaluator::Predicate::Negation.new(
+              Morpher::Evaluator::Predicate::Boolean::Or.new([
+                described_class::SubjectPrefix.new(expression_b)
+              ])
+            )
+          ])
+        end
+
+        it { should eql(expected_matcher) }
+      end
     end
 
     context 'on config with multiple match expressions' do