diff --git a/test/php/library/Businessprocess/Operators/NotOperatorTest.php b/test/php/library/Businessprocess/Operators/NotOperatorTest.php
new file mode 100644
index 0000000..d1fcbe9
--- /dev/null
+++ b/test/php/library/Businessprocess/Operators/NotOperatorTest.php
@@ -0,0 +1,85 @@
+<?php
+
+namespace Tests\Icinga\Module\Businessprocess\Storage;
+
+use Icinga\Module\Businessprocess\BpNode;
+use Icinga\Module\Businessprocess\Test\BaseTestCase;
+use Icinga\Module\Businessprocess\Storage\LegacyStorage;
+
+class NotOperatorTest extends BaseTestCase
+{
+    public function testWhetherNegationsCanBeParsed()
+    {
+        $storage = new LegacyStorage($this->emptyConfigSection());
+        $expressions = array(
+            'a = !b',
+            'a = ! b',
+            'a = b ! c ! d',
+            'a = ! b ! c ! d !',
+        );
+
+        foreach ($expressions as $expression) {
+            $this->assertInstanceOf(
+                'Icinga\\Module\\Businessprocess\\Businessprocess',
+                $storage->loadFromString('dummy', $expression)
+            );
+        }
+    }
+
+    public function testWhetherNegationsMatch()
+    {
+        $storage = new LegacyStorage($this->emptyConfigSection());
+        $expression = 'a = !b';
+        $bp = $storage->loadFromString('dummy', $expression);
+        $a = $bp->getNode('a');
+        $b = $bp->createBp('b')->setState(3);
+        $this->assertEquals(
+            'OK',
+            $a->getStateName()
+        );
+
+        $a->clearState();
+        $b->setState(0);
+        $this->assertEquals(
+            'CRITICAL',
+            $a->getStateName()
+        );
+    }
+
+    public function testWhetherNegatingMultipleValuesBehavesLikeNotAnd()
+    {
+        $storage = new LegacyStorage($this->emptyConfigSection());
+        $expression = 'a = ! b ! c ! d';
+        $bp = $storage->loadFromString('dummy', $expression);
+        $a = $bp->getNode('a');
+        $b = $bp->createBp('b')->setState(3);
+        $c = $bp->createBp('c')->setState(3);
+        $d = $bp->createBp('d')->setState(3);
+        $this->assertEquals(
+            'OK',
+            $a->getStateName()
+        );
+
+        $a->clearState();
+        $b->setState(0);
+        $this->assertEquals(
+            'OK',
+            $a->getStateName()
+        );
+
+        $a->clearState();
+        $c->setState(0);
+        $this->assertEquals(
+            'OK',
+            $a->getStateName()
+        );
+
+        $a->clearState();
+        $d->setState(0);
+        $this->assertEquals(
+            'CRITICAL',
+            $a->getStateName()
+        );
+    }
+}
+