Add fieldValueMatches / fieldValueNotMatches

Would be hand to allow pattern assertions on field values like on the page text.
This was mentioned here #696 but: "PR got lost in the sands of time" :)

src/WebAssert.php

@@ -695,6 +695,44 @@ public function fieldValueNotEquals($field, $value, TraversableElement $containe
         $this->assert(!preg_match($regex, $actual), $message);
     }
 
+    /**
+     * Checks that specific field matches provided regex.
+     *
+     * @param string             $field     field id|name|label|value
+     * @param string             $regex     pattern
+     * @param TraversableElement $container document to check against
+     *
+     * @throws ExpectationException
+     */
+    public function fieldValueMatches($field, $regex, TraversableElement $container = null)
+    {
+        $node = $this->fieldExists($field, $container);
+        $actual = $node->getValue();
+
+        $message = sprintf('The pattern "%s" was not found in the value "%s" of field "%s".', $regex, $actual, $field);
+
+        $this->assert((bool) preg_match($regex, $actual), $message);
+    }
+
+    /**
+     * Checks that specific field have provided value.
+     *
+     * @param string             $field     field id|name|label|value
+     * @param string             $regex     pattern
+     * @param TraversableElement $container document to check against
+     *
+     * @throws ExpectationException
+     */
+    public function fieldValueNotMatches($field, $regex, TraversableElement $container = null)
+    {
+        $node = $this->fieldExists($field, $container);
+        $actual = $node->getValue();
+
+        $message = sprintf('The pattern "%s" was found in the value "%s" of field "%s", but it should not.', $regex, $actual, $field);
+
+        $this->assert((bool) preg_match($regex, $actual), $message);
+    }
+
     /**
      * Checks that specific checkbox is checked.
      *