Add test coverage

Author: engcom-Echo

app/code/Magento/Customer/Test/Unit/Model/Metadata/Form/MultilineTest.php

@@ -94,4 +94,28 @@ public function validateValueLengthDataProvider()
             ]
         );
     }
+
+    /**
+     * @param array $value value to pass to compactValue()
+     * @param string $expected expected output
+     *
+     * @dataProvider compactValueDataProvider
+     */
+    public function testCompactValue($value, $expected)
+    {
+        $this->assertSame($expected, $this->getClass("line")->compactValue($value));
+    }
+
+    /**
+     * @return array
+     */
+    public function compactValueDataProvider()
+    {
+        return [
+            [
+                ["b"=>"element1", "a"=>"element2"],
+                ["element2\nelement1"],
+            ]
+        ];
+    }
 }