test: refactor the code in test-dns-ipv6

* remove the manual control for functions execution
* use common.mustCall to control the functions execution automatically
* use let and const instead of var
* use assert.strictEqual instead assert.equal

PR-URL: https://github.com/nodejs/node/pull/10219
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>

test/internet/test-dns-ipv6.js

@@ -5,8 +5,6 @@ const dns = require('dns');
 const net = require('net');
 const isIPv6 = net.isIPv6;
 
-let expected = 0;
-let completed = 0;
 let running = false;
 const queue = [];
 
@@ -17,7 +15,7 @@ if (!common.hasIPv6) {
 
 function TEST(f) {
   function next() {
-    var f = queue.shift();
+    const f = queue.shift();
     if (f) {
       running = true;
       console.log(f.name);
@@ -27,11 +25,9 @@ function TEST(f) {
 
   function done() {
     running = false;
-    completed++;
     process.nextTick(next);
   }
 
-  expected++;
   queue.push(f);
 
   if (!running) {
@@ -44,46 +40,46 @@ function checkWrap(req) {
 }
 
 TEST(function test_resolve6(done) {
-  var req = dns.resolve6('ipv6.google.com', function(err, ips) {
-    if (err) throw err;
+  const req = dns.resolve6('ipv6.google.com',
+    common.mustCall((err, ips) => {
+      assert.ifError(err);
 
       assert.ok(ips.length > 0);
 
-    for (var i = 0; i < ips.length; i++) {
+      for (let i = 0; i < ips.length; i++)
         assert.ok(isIPv6(ips[i]));
-    }
 
       done();
-  });
+    }));
 
   checkWrap(req);
 });
 
 TEST(function test_reverse_ipv6(done) {
-  var req = dns.reverse('2001:4860:4860::8888', function(err, domains) {
-    if (err) throw err;
+  const req = dns.reverse('2001:4860:4860::8888',
+    common.mustCall((err, domains) => {
+      assert.ifError(err);
 
       assert.ok(domains.length > 0);
 
-    for (var i = 0; i < domains.length; i++) {
-      assert.ok(domains[i]);
+      for (let i = 0; i < domains.length; i++)
         assert.ok(typeof domains[i] === 'string');
-    }
 
       done();
-  });
+    }));
 
   checkWrap(req);
 });
 
 TEST(function test_lookup_ipv6_explicit(done) {
-  var req = dns.lookup('ipv6.google.com', 6, function(err, ip, family) {
-    if (err) throw err;
-    assert.ok(net.isIPv6(ip));
+  const req = dns.lookup('ipv6.google.com', 6,
+    common.mustCall((err, ip, family) => {
+      assert.ifError(err);
+      assert.ok(isIPv6(ip));
       assert.strictEqual(family, 6);
 
       done();
-  });
+    }));
 
   checkWrap(req);
 });
@@ -103,24 +99,24 @@ TEST(function test_lookup_ipv6_implicit(done) {
 */
 
 TEST(function test_lookup_ipv6_explicit_object(done) {
-  var req = dns.lookup('ipv6.google.com', {
+  const req = dns.lookup('ipv6.google.com', {
     family: 6
-  }, function(err, ip, family) {
-    if (err) throw err;
-    assert.ok(net.isIPv6(ip));
+  }, common.mustCall((err, ip, family) => {
+    assert.ifError(err);
+    assert.ok(isIPv6(ip));
     assert.strictEqual(family, 6);
 
     done();
-  });
+  }));
 
   checkWrap(req);
 });
 
 TEST(function test_lookup_ipv6_hint(done) {
-  var req = dns.lookup('www.google.com', {
+  const req = dns.lookup('www.google.com', {
     family: 6,
     hints: dns.V4MAPPED
-  }, function(err, ip, family) {
+  }, common.mustCall((err, ip, family) => {
     if (err) {
       // FreeBSD does not support V4MAPPED
       if (common.isFreeBSD) {
@@ -130,41 +126,43 @@ TEST(function test_lookup_ipv6_hint(done) {
         assert.ok(/getaddrinfo EAI_BADFLAGS/.test(err.message));
         done();
         return;
-      } else {
-        throw err;
       }
+
+      assert.ifError(err);
     }
-    assert.ok(net.isIPv6(ip));
+
+    assert.ok(isIPv6(ip));
     assert.strictEqual(family, 6);
 
     done();
-  });
+  }));
 
   checkWrap(req);
 });
 
 TEST(function test_lookup_ip_ipv6(done) {
-  var req = dns.lookup('::1', function(err, ip, family) {
-    if (err) throw err;
-    assert.ok(net.isIPv6(ip));
+  const req = dns.lookup('::1',
+    common.mustCall((err, ip, family) => {
+      assert.ifError(err);
+      assert.ok(isIPv6(ip));
       assert.strictEqual(family, 6);
 
       done();
-  });
+    }));
 
   checkWrap(req);
 });
 
 TEST(function test_lookup_all_ipv6(done) {
-  var req = dns.lookup(
+  const req = dns.lookup(
     'www.google.com',
     {all: true, family: 6},
-    function(err, ips) {
-      if (err) throw err;
+    common.mustCall((err, ips) => {
+      assert.ifError(err);
       assert.ok(Array.isArray(ips));
       assert.ok(ips.length > 0);
 
-      ips.forEach(function(ip) {
+      ips.forEach((ip) => {
         assert.ok(isIPv6(ip.address),
                   'Invalid IPv6: ' + ip.address.toString());
         assert.strictEqual(ip.family, 6);
@@ -172,24 +170,25 @@ TEST(function test_lookup_all_ipv6(done) {
 
       done();
     }
-  );
+  ));
 
   checkWrap(req);
 });
 
 TEST(function test_lookupservice_ip_ipv6(done) {
-  var req = dns.lookupService('::1', 80, function(err, host, service) {
+  const req = dns.lookupService('::1', 80,
+    common.mustCall((err, host, service) => {
       if (err) {
         // Not skipping the test, rather checking an alternative result,
         // i.e. that ::1 may not be configured (e.g. in /etc/hosts)
         assert.strictEqual(err.code, 'ENOTFOUND');
         return done();
       }
-    assert.equal(typeof host, 'string');
+      assert.strictEqual(typeof host, 'string');
       assert(host);
       assert(['http', 'www', '80'].includes(service));
       done();
-  });
+    }));
 
   checkWrap(req);
 });
@@ -206,9 +205,3 @@ TEST(function test_lookupservice_ip_ipv6(done) {
 
   checkWrap(req);
 }); */
-
-process.on('exit', function() {
-  console.log(completed + ' tests completed');
-  assert.equal(running, false);
-  assert.strictEqual(expected, completed);
-});