Update unit test for direct callgraph

Add a node with no edges to the test and check that it does the right
thing

Author: Owen Jones

unit/analyses/call_graph.cpp

@@ -64,6 +64,7 @@ SCENARIO("call_graph",
     // }
     // void C() { }
     // void D() { }
+    // void E() { }
 
     goto_modelt goto_model;
     code_typet void_function_type;
@@ -101,6 +102,8 @@ SCENARIO("call_graph",
       create_void_function_symbol("C", code_skipt()));
     goto_model.symbol_table.add(
       create_void_function_symbol("D", code_skipt()));
+    goto_model.symbol_table.add(
+      create_void_function_symbol("E", code_skipt()));
 
     stream_message_handlert msg(std::cout);
     goto_convert(goto_model, msg);
@@ -183,6 +186,11 @@ SCENARIO("call_graph",
       for(node_indext i=0; i<exported.size(); ++i)
         nodes_by_name[exported[i].function]=i;
 
+      THEN("We expect 5 nodes")
+      {
+        REQUIRE(exported.size() == 5);
+      }
+
       THEN("We expect edges A -> { A, B }, B -> { C, D }")
       {
         // Note that means the extra A -> B edge has gone away (the grapht
@@ -228,6 +236,14 @@ SCENARIO("call_graph",
         REQUIRE(predecessors.count("B"));
         REQUIRE(predecessors.count("D"));
       }
+
+      THEN("We expect {E} to be able to reach E")
+      {
+        std::set<irep_idt> predecessors =
+          get_reaching_functions(exported, "E");
+        REQUIRE(predecessors.size() == 1);
+        REQUIRE(predecessors.count("E"));
+      }
     }
 
     WHEN("The call graph, with call sites, is exported as a grapht")
@@ -241,6 +257,11 @@ SCENARIO("call_graph",
       for(node_indext i=0; i<exported.size(); ++i)
         nodes_by_name[exported[i].function]=i;
 
+      THEN("We expect 5 nodes")
+      {
+        REQUIRE(exported.size() == 5);
+      }
+
       THEN("We expect edges A -> { A, B }, B -> { C, D }")
       {
         // Note that means the extra A -> B edge has gone away (the grapht