WP mu-plugin for testing HTTP error codes

gistfile1.txt

<?php

if( isset( $_GET['code'] ) && isset( $_GET['error'] ) ) {
    add_action('send_headers', 'error_test_check_headers');
}

function error_test_check_headers() {
    $codes = error_test_get_codes();
    $code = $_GET['code'];

    if( ! isset( $codes[$code] ) ) {
        return;
    }

    $header_string = "HTTP/1.0 " . $codes[$code];
    @header($header_string);
    exit();
}


function error_test_get_codes() {
    return [
        "400" => "400 Bad Request",
        "401" => "401 Unauthorized",
        "402" => "402 Payment Required",
        "403" => "403 Forbidden",
        "404" => "404 Not Found",
        "405" => "405 Method Not Allowed",
        "406" => "406 Not Acceptable",
        "407" => "407 Proxy Authentication Required",
        "408" => "408 Request Timeout",
        "409" => "409 Conflict",
        "410" => "410 Gone",
        "411" => "411 Length Required",
        "412" => "412 Precondition Failed",
        "413" => "413 Payload Too Large",
        "414" => "414 URI Too Long",
        "415" => "415 Unsupported Media Type",
        "416" => "416 Requested Range Not Satisfiable",
        "417" => "417 Expectation Failed",
        "418" => "418 I'm a teapot",
        "421" => "421 Misdirected Request",
        "422" => "422 Unprocessable Entity",
        "423" => "423 Locked",
        "424" => "424 Failed Dependency",
        "425" => "425 Too Early",
        "426" => "426 Upgrade Required",
        "428" => "428 Precondition Required",
        "429" => "429 Too Many Requests",
        "431" => "431 Request Header Fields Too Large",
        "451" => "451 Unavailable For Legal Reasons",
        "500" => "500 Internal Server Error",
        "501" => "501 Not Implemented",
        "502" => "502 Bad Gateway",
        "503" => "503 Service Unavailable",
        "504" => "504 Gateway Timeout",
        "505" => "505 HTTP Version Not Supported",
        "506" => "506 Variant Also Negotiates",
        "507" => "507 Insufficient Storage",
        "508" => "508 Loop Detected",
        "510" => "510 Not Extended",
        "511" => "511 Network Authentication Required",
    ];
}