Relax testing of graph handing in Queryable specs

`Queryable` shared examples failed for `Graph`s with a non-default graph
name. They required the graph to retain the query pattern's
`graph_name`, which is undesirable behavior. Instead `Graph` replaces
the provided `graph_name` with its own, when querying, mimicking its
behavior on write operations.

This relaxes the specs to allow for the special case of a queryable
scoped in this way.

Author: Tom Johnson

lib/rdf/spec/queryable.rb

@@ -89,22 +89,27 @@
           pattern = RDF::Query::Pattern.new(nil, nil, nil, graph_name: false)
           solutions = []
           subject.send(method, pattern) {|s| solutions << s}
-          named_statements = subject.statements.reject {|st| st.has_name?}.length
-          expect(solutions.size).to eq named_statements
+
+          named_statements = subject.statements
+          named_statements.reject! {|st| st.has_name?} unless
+            subject.respond_to?(:graph_name) && !subject.graph_name.nil?
+
+          expect(solutions.size).to eq named_statements.size
         end
 
-        it "returns statements from named graphss with variable graph_name" do
+        it "returns statements from named graphs with variable graph_name" do
           unless subject.graph_names.to_a.empty?
             pattern = RDF::Query::Pattern.new(nil, nil, nil, graph_name: :c)
             solutions = []
             subject.send(method, pattern) {|s| solutions << s}
-            named_statements = subject.statements.select {|st| st.has_name?}.length
-            expect(solutions.size).to eq named_statements
+            named_statements = subject.statements.select {|st| st.has_name?}
+            expect(solutions.size).to eq named_statements.size
           end
         end
 
         it "returns statements from specific graph with URI graph_name" do
-          unless subject.graph_names.to_a.empty?
+          unless subject.graph_names.to_a.empty? || 
+                 (subject.respond_to?(:graph_name) && !subject.graph_name.nil?)
             pattern = RDF::Query::Pattern.new(nil, nil, nil, graph_name: RDF::URI("http://ar.to/#self"))
             solutions = []
             subject.send(method, pattern) {|s| solutions << s}