function testContainsValidChars() { $this->assertTrue(Isbn::containsValidChars('1234567890')); $this->assertTrue(Isbn::containsValidChars('978-3-86680-192-9')); $this->assertTrue(Isbn::containsValidChars('978 3 86680 192 9')); $this->assertFalse(Isbn::containsValidChars('12345678')); $this->assertFalse(Isbn::containsValidChars('978 3 86680 192 99')); }