Use typehinting instead of throwing exception.

src/ORM/Table.php

@@ -393,16 +393,12 @@ public function registryAlias($registryAlias = null)
      * @param \Cake\Database\Connection|null $conn The new connection instance
      * @return \Cake\Database\Connection
      */
-    public function connection($conn = null)
+    public function connection(Connection $conn = null)
     {
         if ($conn === null) {
             return $this->_connection;
         }
 
-        if (!($conn instanceof Connection)) {
-            throw new RuntimeException('$conn must be an instance of \Cake\Database\Connection');
-        }
-
         return $this->_connection = $conn;
     }
 

tests/TestCase/ORM/TableTest.php

@@ -185,19 +185,6 @@ public function testConnection()
         $this->assertSame($this->connection, $table->connection());
     }
 
-    /**
-     * Tests exception is thrown in connection is not instance of
-     * \Cake\Database\Connection
-     *
-     * @expectedException \RuntimeException
-     * @expectedExceptionMessage $conn must be an instance of \Cake\Database\Connection
-     * @return void
-     */
-    public function testConnectionException()
-    {
-        $table = new Table(['table' => 'users', 'connection' => 'default']);
-    }
-
     /**
      * Tests primaryKey method
      *