Add tests for symbol conversion

spec/facter_db_spec.rb

@@ -325,6 +325,19 @@
 
     context 'without parameters' do
       include_examples 'returns a result'
+      it 'returns symbols as keys in factsets' do
+        result.each do |factset|
+          expect(factset.keys).to all(be_an_instance_of(Symbol))
+        end
+      end
+    end
+    context 'with stringified output' do
+      let(:symbolize_keys) {false}
+      it 'returns strings as keys in factsets' do
+        result.each do |factset|
+          expect(factset.keys).to all(be_an_instance_of(String))
+        end
+      end
     end
 
     context 'with an Array filter' do