diff --git a/tests/tool.phpt b/tests/tool.phpt
index 6745901..1114d94 100644
--- a/tests/tool.phpt
+++ b/tests/tool.phpt
@@ -4,10 +4,12 @@ declare(strict_types=1);
 
 namespace Dakujem\Test;
 
+use ArrayIterator;
 use Dakujem\Oliva\Iterator\LevelOrderTraversal;
 use Dakujem\Oliva\Iterator\PostOrderTraversal;
 use Dakujem\Oliva\Iterator\PreOrderTraversal;
 use Dakujem\Oliva\Node;
+use Dakujem\Oliva\Seed;
 use Tester\Assert;
 
 require_once __DIR__ . '/setup.php';
@@ -43,4 +45,21 @@ require_once __DIR__ . '/setup.php';
     Assert::same('FBADCEGIH', TreeTesterTool::flatten($tree, PreOrderTraversal::class));
     Assert::same('ACEDBHIGF', TreeTesterTool::flatten($tree, PostOrderTraversal::class));
     Assert::same('FBGADICEH', TreeTesterTool::flatten($tree, LevelOrderTraversal::class));
-})();
\ No newline at end of file
+})();
+
+(function () {
+    Assert::same(null, Seed::firstOf([]));
+    Assert::same(1, Seed::firstOf([1]));
+    Assert::same(1, Seed::firstOf([1, 2, 3]));
+    Assert::same(1, Seed::firstOf(new ArrayIterator([1, 2, 3])));
+    Assert::same(null, Seed::firstOf(new ArrayIterator([])));
+    Assert::same(42, Seed::firstOf(new ArrayIterator([42])));
+})();
+
+(function () {
+    Assert::same([], iterator_to_array(Seed::merged()));
+    Assert::same([], iterator_to_array(Seed::merged([], [], new ArrayIterator([]))));
+    Assert::same([1, 2, 3, 4], iterator_to_array(Seed::merged([1, 2], new ArrayIterator([2 => 3, 4]))));
+    Assert::same([1, 2, 3, 4], iterator_to_array(Seed::merged(new ArrayIterator([1, 2]), new ArrayIterator([2 => 3, 4]))));
+    Assert::same([1, 2, 3, 4], iterator_to_array(Seed::merged(new ArrayIterator([1, 2]), [2 => 3, 4])));
+})();