Add tests.

spec/drupol/phptree/Modifier/FulfillCapacitySpec.php

@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace spec\drupol\phptree\Modifier;
+
+use drupol\phptree\Modifier\FulfillCapacity;
+use drupol\phptree\Node\ValueNode;
+use PhpSpec\ObjectBehavior;
+
+class FulfillCapacitySpec extends ObjectBehavior
+{
+    public function it_can_fulfill_missing_node()
+    {
+        $tree = new ValueNode('root', 10);
+
+        $nodes = [];
+
+        foreach (range('A', 'E') as $value) {
+            $nodes[] = new ValueNode($value);
+        }
+        $tree->add(...$nodes);
+
+        $this
+            ->modify($tree)
+            ->count()
+            ->shouldReturn(10);
+    }
+
+    public function it_is_initializable()
+    {
+        $this->shouldHaveType(FulfillCapacity::class);
+    }
+}

spec/drupol/phptree/Modifier/RemoveNullNodeSpec.php

@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace spec\drupol\phptree\Modifier;
+
+use drupol\phptree\Modifier\RemoveNullNode;
+use drupol\phptree\Node\ValueNode;
+use PhpSpec\ObjectBehavior;
+
+class RemoveNullNodeSpec extends ObjectBehavior
+{
+    public function it_can_remove_node_with_null_values()
+    {
+        $tree = new ValueNode('root', 10);
+
+        $nodes = [];
+
+        foreach ([null, null, null, 'a', 'b', null, 'c'] as $value) {
+            $nodes[] = new ValueNode($value);
+        }
+        $tree->add(...$nodes);
+
+        $this
+            ->modify($tree)
+            ->count()
+            ->shouldReturn(3);
+    }
+
+    public function it_is_initializable()
+    {
+        $this->shouldHaveType(RemoveNullNode::class);
+    }
+}