MAGETWO-46206: Fix random fails of Magento\Checkout\Test\TestCase\OnePageCheckoutTest functional test

 - fixed fields order for shipping address form

Author: Serhiy Shkolyarenko

dev/tests/functional/tests/app/Magento/Checkout/Test/Block/Cart/Shipping.php

@@ -45,6 +45,7 @@ class Shipping extends Form
 
     /**
      * Fields that are used in estimation shipping form.
+     * Indexes of this array should be numeric, they are used in compare() method.
      *
      * @var array
      */
@@ -91,6 +92,29 @@ public function selectShippingMethod(array $shipping)
         }
     }
 
+    /**
+     * Compare elements according to $this->estimationFields order
+     *
+     * @param $a
+     * @param $b
+     * @return int
+     */
+    public function compare($a, $b)
+    {
+        $a = array_search($a, $this->estimationFields);
+        $b = array_search($b, $this->estimationFields);
+        switch (true) {
+            case false !== $a && false !== $b:
+                return $a - $b;
+            case false !== $a:
+                return -1;
+            case false !== $b:
+                return 1;
+            default:
+                return 0;
+        }
+    }
+
     /**
      * Fill shipping and tax form.
      *
@@ -102,6 +126,8 @@ public function fillEstimateShippingAndTax(Address $address)
         $this->openEstimateShippingAndTax();
         $data = $address->getData();
         $mapping = $this->dataMapping(array_intersect_key($data, array_flip($this->estimationFields)));
+        // sort array according to $this->estimationFields element order
+        uksort($mapping, [$this, 'compare']);
 
         // Test environment may become unstable when form fields are filled in a default manner.
         // Imitating behavior closer to the real user.