add Countries::validateCountryCode method

src/Countries.php

@@ -12,6 +12,9 @@
  */
 class Countries {
 
+    /**
+     * @var array List of ISO-3166-1-alpha2 country-codes + names
+     */
     private static $all = [
         'AF' => 'Afghanistan',
         'AX' => 'Aland Islands',
@@ -292,7 +295,7 @@ class Countries {
     ];
 
     /**
-     * Get all countries in code => name format
+     * Get all countries in ISO-3166-1-alpha2 country code => name format
      *
      * @return array
      */
@@ -344,8 +347,21 @@ public function inEurope(string $code) : bool
         return in_array($code, self::$eu);
     }
 
+
+    /**
+     * Checks whether the given string is a valid public IPv4 or IPv6 address
+     * 
+     * @param string $countryCode
+     * @return bool
+     */
+    public function validateCountryCode(string $countryCode) : bool
+    {
+        return isset(self::$all[$countryCode]);
+    }
+
+
     /**
-     * Checks whether the given string is a valid public IP address
+     * Checks whether the given string is a valid public IPv4 or IPv6 address
      * 
      * @param string $ipAddress
      * @return bool

tests/CountriesTest.php

@@ -51,6 +51,23 @@ public function testValidateIpAddress() {
         }
     }
 
+    /**
+     * @covers Countries::validateCountryCode
+     */
+    public function testValidateCountryCode() {
+        $countries = new Countries();
+        $map = [
+            'foo' => false,
+            '' => false,
+            'NL' => true,
+            'US' => true,
+        ];
+
+        foreach($map as $input => $expected) {
+            self::assertEquals($expected, $countries->validateCountryCode($input));
+        }
+    }
+
      /**
      * @covers Countries::ip
      */