Test default false graph name

We don't want transactions to overwrite `false` graph names.

Author: Tom Johnson

lib/rdf/spec/transaction.rb

@@ -127,6 +127,27 @@
         expect(subject.repository).not_to have_statement(with_name)
         expect(subject.repository).to have_statement(st)
       end
+
+      it 'retains existing graph names' do
+        st.graph_name = RDF::URI('g')
+        repository.insert(st)
+        
+        expect do 
+          subject.delete(st)
+          subject.execute
+        end.to change { subject.repository.statements }.to be_empty
+      end
+
+      it 'retains existing default graph name' do
+        st.graph_name = false
+
+        repository.insert(st)
+        
+        expect do 
+          subject.delete(st)
+          subject.execute
+        end.to change { subject.repository.statements }.to be_empty
+      end
     end
   end
 
@@ -189,6 +210,17 @@
 
         expect(subject.repository).to have_statement(st)
       end
+
+      it 'retains existing default graph name' do
+        st.graph_name = false
+        
+        expect do 
+          subject.insert(st)
+          subject.execute
+        end.to change { subject.repository.statements }
+
+        expect(subject.repository).to have_statement(st)
+      end
     end
   end