Closes #9

tests/tree_node_test.cpp

@@ -0,0 +1,33 @@
+// Standalone C++17 test: no Qt required.
+#include "dbc_tree_builder.h"
+#include <stdexcept>
+#include <type_traits>
+
+static void Check(bool condition) {
+    if (!condition) throw std::runtime_error("Tree navigation test failed");
+}
+
+int main() {
+    static_assert(!std::is_move_constructible<TreeNode>::value, "Node addresses must be stable");
+    DbcDatabase database;
+    FrameInfo frame;
+    SignalInfo signal;
+    frame.signals.push_back(signal);
+    frame.signals.push_back(signal);
+    database.frames.push_back(frame);
+    database.frames.push_back(frame);
+    auto root = DbcTreeBuilder().Build(database);
+    Check(root->GetParent() == nullptr && root->GetRow() == 0);
+    root->AddChild(nullptr);
+    Check(root->GetChildCount() == 2 && !root->GetChild(2));
+    for (std::size_t row = 0; row < root->GetChildCount(); ++row) {
+        const TreeNode *child = root->GetChild(row);
+        Check(child->GetParent() == root.get() && child->GetRow() == row);
+        for (std::size_t position = 0; position < child->GetChildCount(); ++position) {
+            const TreeNode *leaf = child->GetChild(position);
+            Check(leaf->GetParent() == child && leaf->GetRow() == position);
+        }
+    }
+    auto transferred = std::move(root);
+    Check(transferred->GetChild(0)->GetParent() == transferred.get());
+}