Merge branch 'fix-rr'

docs/Validation.md

+Validation
+==========
+
+Very little validation is done automatically when setting RData or Resource Record objects, so the onus is on the
+implementor to validate the resource data and the zone record. Contained within the library, however, are some useful
+validation tools. These are static functions contained within `Badcow\DNS\Validator` (here, simply referred to as
+`Validator`).
+
+## Validate the Zone
+`Validator::zone()` will inspect a number of properties of a Zone, namely:
+ * There is exactly one SOA record,
+ * There are NS records, and
+ * There is exactly one record class (while it is permissible to use obsolete classes such as CHAOS, in all modern
+ contexts, this is always IN).
+
+The return value is a binary sum of error codes which can be determined using boolean operands. A valid zone will
+return `0`, AKA `Validator::ZONE_OKAY`. _Exempli gratia:_
+```php
+$zone //Some Badcow\DNS\Zone
+if (Validator::zone($zone) & Validator::ZONE_NO_SOA) echo "There are no SOA Records";
+if (Validator::zone($zone) & Validator::ZONE_TOO_MANY_CLASSES) echo "There are too many classes."; 
+```
+
+The return codes are:
+ * `ZONE_NO_SOA`
+ * `ZONE_TOO_MANY_SOA`
+ * `ZONE_NO_NS`
+ * `ZONE_NO_CLASS`
+ * `ZONE_TOO_MANY_CLASSES`
+ * `ZONE_OKAY`
+

tests/ResourceRecordTest.php

@@ -51,4 +51,16 @@ class ResourceRecordTest extends TestCase
         $this->assertEquals($comment, $rr->getComment());
         $this->assertEquals($a->getType(), $rr->getType());
     }
+    
+    public function testUnsetTtl()
+    {
+        $rr = new ResourceRecord('example.com.');
+        $ttl = 10800;
+
+        $this->assertNull($rr->getTtl());
+        $rr->setTtl($ttl);
+        $this->assertEquals($ttl, $rr->getTtl());
+        $rr->setTtl(null);
+        $this->assertNull($rr->getTtl());
+    }
 }