Avoid changing Repository while tx is in progress

Adding or deleting statements in the Repository causes serializable
transactions to break (correctly). Instead, prepare the repository state
before beginning the test transaction.

Author: Tom Johnson

lib/rdf/spec/transaction.rb

@@ -79,7 +79,7 @@
     let(:st) { RDF::Statement(:s, RDF::URI('p'), 'o') }
 
     it 'adds to deletes' do
-      subject.repository.insert(st)
+      repository.insert(st)
 
       expect do 
         subject.delete(st)
@@ -89,7 +89,7 @@
 
     it 'adds multiple to deletes' do
       sts = [st] << RDF::Statement(:x, RDF::URI('y'), 'z')
-      subject.repository.insert(*sts)
+      repository.insert(*sts)
 
       expect do
         subject.delete(*sts)
@@ -100,7 +100,7 @@
     it 'adds enumerable to deletes' do
       sts = [st] << RDF::Statement(:x, RDF::URI('y'), 'z')
       sts.extend(RDF::Enumerable)
-      subject.repository.insert(sts)
+      repository.insert(sts)
 
       expect do
         subject.delete(sts)
@@ -114,10 +114,10 @@
       let(:graph_uri) { RDF::URI('http://example.com/graph_1') }
 
       it 'adds the graph_name to statements' do
-        subject.repository.insert(st)
+        repository.insert(st)
         with_name = st.dup
         with_name.graph_name = graph_uri
-        subject.repository.insert(with_name)
+        repository.insert(with_name)
 
         expect do 
           subject.delete(st)