NEW: WithMockTime callback.

src/ORM/FieldType/DBDatetime.php

@@ -209,6 +209,27 @@ class DBDatetime extends DBDate implements TemplateGlobalProvider
         self::$mock_now = null;
     }
 
+    /**
+     * Run a callback with specific time, original mock value is retained after callback
+     *
+     * @param DBDatetime|string $time
+     * @param callable $callback
+     * @return mixed
+     * @throws Exception
+     */
+    public static function withFixedNow($time, $callback)
+    {
+        $original = self::$mock_now;
+
+        try {
+            self::set_mock_now($time);
+
+            return $callback();
+        } finally {
+            self::$mock_now = $original;
+        }
+    }
+
     public static function get_template_global_variables()
     {
         return [

tests/php/ORM/DBDatetimeTest.php

@@ -42,6 +42,22 @@ class DBDatetimeTest extends SapphireTest
         $this->assertEquals($systemDatetime->Date(), $nowDatetime->Date());
     }
 
+    public function testFixedNow()
+    {
+        $mockDate1 = '2010-01-01 10:00:00';
+        $mockDate2 = '2011-01-01 10:00:00';
+
+        DBDatetime::withFixedNow($mockDate1, function () use ($mockDate1, $mockDate2) {
+            $this->assertEquals($mockDate1, DBDatetime::now()->Rfc2822());
+
+            DBDatetime::withFixedNow($mockDate2, function () use ($mockDate2) {
+                $this->assertEquals($mockDate2, DBDatetime::now()->Rfc2822());
+            });
+
+            $this->assertEquals($mockDate1, DBDatetime::now()->Rfc2822());
+        });
+    }
+
     public function testSetNullAndZeroValues()
     {
         $date = DBDatetime::create_field('Datetime', '');