/**
  * Test the validity of postcode letter
  */
 public function testPostcodeLetter()
 {
     $postcodeLetter = $this->faker->randomPostcodeLetter();
     $this->assertNotEmpty($postcodeLetter);
     $this->assertInternalType('string', $postcodeLetter);
     $this->assertRegExp('/^[A-Z]{1}$/', $postcodeLetter);
 }