Add core graph member functions

test/graph_test.cc

@@ -0,0 +1,26 @@
+#include <doctest/doctest.h>
+
+#include <cstdint>
+
+#include "include/graph.h"
+
+TEST_SUITE("Testing Graph.") {
+  using namespace graph;
+
+  TEST_CASE("Insert vertices/edges.") {
+    Graph<std::uint16_t> G;
+
+    G.insert(1, 2);
+    G.insert(1, 4);
+    G.insert(1, 6);
+    G.insert(2, 4);
+    G.insert(2, 5);
+    G.insert(3, 4);
+    G.insert(3, 6);
+    G.insert(4, 6);
+    G.insert(5, 6);
+
+    // CHECK_EQ(G.connected(1, 5), true);
+
+  }
+}

test/main.cc

@@ -0,0 +1,2 @@
+#define DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
+#include <doctest/doctest.h>