Test that show_blocklist() outputs parsed domains to stdout.

-- Testcase --
import adb from 'adblock-fast';
import { popen } from 'fs';
let ti = adb._test_internals;

// Build the blocklist
adb.env.load_config();
ti.set_cfg('dns', 'dnsmasq.servers');
ti.set_cfg('dnsmasq_sanity_check', false);
ti.set_cfg('dnsmasq_validity_check', false);
ti.set_cfg('heartbeat_domain', null);
ti.set_cfg('config_update_enabled', false);
ti.set_cfg('update_config_sizes', false);
ti.env.dns_set_output_values('dnsmasq.servers');
ti.append_urls();
ti.download_lists();

// show_blocklist() uses system() to run sed parse_filter on the output file,
// which outputs plain domains to stdout. Count lines and check a few domains.
let cmd = sprintf("sed '%s' %s", ti.dns_output.parse_filter, ti.dns_output.file);
let p = popen(cmd, 'r');
let out = p ? (p.read('all') || '') : '';
if (p) p.close();

let domains = filter(split(out, '\n'), l => length(l) > 0);
let count = length(domains);

let must_have = [
	'ad.doubleclick.test.example.com',
	'common-shared-1.test.example.com',
	'adhost-zero-1.test.example.org',
];

let domain_set = {};
for (let d in domains) domain_set[d] = true;

let results = [];
push(results, sprintf('domain_count: %d', count));
for (let d in must_have) {
	push(results, sprintf('%s: %s', d, domain_set[d] ? 'PRESENT' : 'MISSING'));
}

print(join('\n', results) + '\n');
-- End --

-- Expect stdout --
domain_count: 162
ad.doubleclick.test.example.com: PRESENT
common-shared-1.test.example.com: PRESENT
adhost-zero-1.test.example.org: PRESENT
-- End --