Fixed https://github.com/eclipse/xacc/issues/486

Signed-off-by: Thien Nguyen <nguyentm@ornl.gov>

quantum/gate/ir/Circuit.cpp

@@ -199,7 +199,7 @@ void Circuit::load(std::istream &inStream) {
   }
 }
 
-const int Circuit::depth() { return toGraph()->depth() - 2; }
+const int Circuit::depth() { return toGraph()->depth(); }
 
 const std::string Circuit::persistGraph() {
   std::stringstream s;

quantum/gate/utils/tests/IRToGraphVisitorTester.cpp

@@ -61,6 +61,7 @@ TEST(IRToGraphTester, checkSimple) {
 
   EXPECT_EQ(graph->getVertexProperties(5).getString("name"), z->name());
   EXPECT_EQ(graph->getVertexProperties(5).get<int>("layer"), 2);
+  EXPECT_EQ(f->depth(), 3);
 }
 
 TEST(IRToGraphTester, checkCNOTLadder) {
@@ -92,6 +93,15 @@ TEST(IRToGraphTester, checkCNOTLadder) {
     EXPECT_EQ(node.getString("name"), "CNOT");
     EXPECT_EQ(node.get<int>("layer"), i - 1);
   }
+  EXPECT_EQ(f->depth(), 4);
+}
+
+TEST(IRToGraphTester, checkSingleGate) {
+  auto f = std::make_shared<Circuit>("foo");
+  auto x = std::make_shared<X>(0);
+  f->addInstruction(x);
+  f->toGraph()->write(std::cout);
+  EXPECT_EQ(f->depth(), 1);
 }
 
 int main(int argc, char **argv) {