Adding DAG visitor and some unit tests around its function

tests/unit_dag_visitor.cpp

@@ -0,0 +1,34 @@
+#include <iostream>
+
+#include "daggy/DAGVisitor.hpp"
+
+#include "catch.hpp"
+
+TEST_CASE("DAG Visitor Tests", "[dagvisitor]") {
+    daggy::DAG<int> dag;
+
+    REQUIRE_NOTHROW(dag.addVertex(0));
+    for (int i = 1; i < 10; ++i) {
+      dag.addVertex(i);
+      dag.addEdge(i-1, i);
+    }
+
+    // Add an edge to make it interesting
+    dag.addEdge(5, 7);
+
+    // for (auto v : dag.getRoots()) std::cout << " " << v << std::endl;
+
+    SECTION("Basic traversal") {
+      daggy::DAGVisitor visitor(dag);
+      REQUIRE(! visitor.isComplete());
+
+      size_t i = 0;
+      while (! visitor.isComplete()) {
+        auto id = visitor.visitNext();
+        REQUIRE(id.has_value());
+        visitor.completeVisit(id.value());
+        ++i;
+      }
+      REQUIRE(i == 10);
+    }
+}