diff --git a/tests/implementation.phpt b/tests/implementation.phpt
new file mode 100644
index 0000000..c101f67
--- /dev/null
+++ b/tests/implementation.phpt
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Dakujem\Test;
+
+use Dakujem\Oliva\DataNodeContract;
+use Dakujem\Oliva\TreeNodeContract;
+use Tester\Assert;
+
+require_once __DIR__ . '/setup.php';
+
+// TODO test other implementations than `Node` (to test compliance)
+
+
+class BareNode implements TreeNodeContract
+{
+    public function parent(): ?TreeNodeContract
+    {
+        // TODO: Implement parent() method.
+    }
+
+    public function children(): iterable
+    {
+        // TODO: Implement children() method.
+    }
+
+    public function hasChild(int|string|TreeNodeContract $child): bool
+    {
+        // TODO: Implement hasChild() method.
+    }
+
+    public function child(int|string $key): ?TreeNodeContract
+    {
+        // TODO: Implement child() method.
+    }
+
+    public function childKey(TreeNodeContract $node): string|int|null
+    {
+        // TODO: Implement childKey() method.
+    }
+
+    public function isLeaf(): bool
+    {
+        // TODO: Implement isLeaf() method.
+    }
+
+    public function isRoot(): bool
+    {
+        // TODO: Implement isRoot() method.
+    }
+
+    public function root(): TreeNodeContract
+    {
+        // TODO: Implement root() method.
+    }
+
+}
+
+(function () {
+    $a = new BareNode();
+    Assert::type(TreeNodeContract::class, $a);
+    Assert::false($a instanceof DataNodeContract);
+})();
+