u01: Add test case for very short loop

This actually worked, but it is nice to have it verified nonetheless.

u01/tests.cpp

@@ -178,6 +178,30 @@ TEST_CASE("Cycle detection (iterative)") {
   delete n;
 }
 
+TEST_CASE("Very short cycle detection") {
+  node *n = new node("foo");
+  n->add_child(n);
+
+  std::stringstream output;
+  output << n->print_recursive();
+
+  REQUIRE(output.str() == "foo [↝ foo]\n");
+
+  delete n;
+}
+
+TEST_CASE("Very short cycle detection (iterative)") {
+  node *n = new node("foo");
+  n->add_child(n);
+
+  std::stringstream output;
+  output << n->print_iterative();
+
+  REQUIRE(output.str() == "foo [↝ foo]\n");
+
+  delete n;
+}
+
 TEST_CASE("Equivalence of iterative and recursive print") {
   node *n = new node();
   REQUIRE(n->print_recursive() == n->print_iterative());