(GH-140) Fix unit tests for zero resource node graph

Previously in commit 30e8fecb683 an error message was raised for node graphs
with no resources however the unit tests were not modified for this scenario.
This commit updates the unit tests for these test scenarios.

spec/spec_helper.rb

@@ -55,6 +55,12 @@ def close_connection
   end
 end
 
+class MockRelationshipGraph
+  attr_accessor :vertices
+  def initialize()
+  end
+end
+
 class MockResource
   attr_accessor :title
 

spec/unit/puppet-languageserver/message_router_spec.rb

@@ -212,22 +212,47 @@
       end
 
       context 'and successfully generate the node graph' do
-        let(:relationship_graph) { double('graph') }
+        let(:relationship_graph) { MockRelationshipGraph.new() }
         before(:each) do
-          expect(relationship_graph).to receive(:to_dot).with(Hash).and_return(dot_content)
           expect(PuppetLanguageServer::PuppetParserHelper).to receive(:compile_to_pretty_relationship_graph).with(file_content).and_return(relationship_graph)
         end
 
-        it 'should reply with dotContent' do
-          expect(request).to receive(:reply_result).with(hash_including('dotContent' => dot_content))
+        context 'with one or more resources' do
+          before(:each) do
+            relationship_graph.vertices = [double('node1'),double('node2')]
+            expect(relationship_graph).to receive(:to_dot).with(Hash).and_return(dot_content)
+          end
 
-          subject.receive_request(request)
+          it 'should reply with dotContent' do
+            expect(request).to receive(:reply_result).with(hash_including('dotContent' => dot_content))
+
+            subject.receive_request(request)
+          end
+
+          it 'should not reply with error' do
+            expect(request).to_not receive(:reply_result).with(hash_including('error'))
+
+            subject.receive_request(request)
+          end
         end
 
-        it 'should not reply with error' do
-          expect(request).to_not receive(:reply_result).with(hash_including('error'))
+        context 'with zero resources' do
+          before(:each) do
+            relationship_graph.vertices = []
+            expect(relationship_graph).to receive(:to_dot).with(Hash).never
+          end
 
-          subject.receive_request(request)
+          it 'should reply with the error text' do
+            expect(request).to receive(:reply_result).with(hash_including('error' => /no resources/))
+
+            subject.receive_request(request)
+          end
+
+          it 'should not reply with dotContent' do
+            expect(request).to_not receive(:reply_result).with(hash_including('dotContent'))
+
+            subject.receive_request(request)
+          end
         end
       end
     end