test: increase coverage of dns-lookup

Rename `test-dns-lookup-cb-error.js` to `test-dns-lookup.js`.
lookup: https://github.com/nodejs/node/blob/master/lib/dns.js#L105.
Coverage: https://coverage.nodejs.org/coverage-57f6a106fbc69a47/root/dns.js.html

test/parallel/test-dns-lookup.js

@@ -0,0 +1,89 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const cares = process.binding('cares_wrap');
+const dns = require('dns');
+
+// Stub `getaddrinfo` to *always* error.
+cares.getaddrinfo = () => process.binding('uv').UV_ENOENT;
+
+assert.throws(() => {
+  dns.lookup(1, {});
+}, /^TypeError: Invalid arguments: hostname must be a string or falsey$/);
+
+assert.throws(() => {
+  dns.lookup(false, 'cb');
+}, /^TypeError: Invalid arguments: callback must be passed$/);
+
+assert.throws(() => {
+  dns.lookup(false, 'options', 'cb');
+}, /^TypeError: Invalid arguments: callback must be passed$/);
+
+assert.throws(() => {
+  dns.lookup(false, {
+    hints: 100,
+    family: 0,
+    all: false
+  }, () => {});
+}, /^TypeError: Invalid argument: hints must use valid flags$/);
+
+assert.throws(() => {
+  dns.lookup(false, {
+    hints: 0,
+    family: 20,
+    all: false
+  }, () => {});
+}, /^TypeError: Invalid argument: family must be 4 or 6$/);
+
+assert.doesNotThrow(() => {
+  dns.lookup(false, {
+    hints: 0,
+    family: 0,
+    all: true
+  }, common.mustCall((error, result, addressType) => {
+    assert.ifError(error);
+    assert.deepStrictEqual(result, []);
+    assert.strictEqual(addressType, undefined);
+  }));
+});
+
+assert.doesNotThrow(() => {
+  dns.lookup('127.0.0.1', {
+    hints: 0,
+    family: 4,
+    all: true
+  }, common.mustCall((error, result, addressType) => {
+    assert.ifError(error);
+    assert.deepStrictEqual(result, [{
+      address: '127.0.0.1',
+      family: 4
+    }]);
+    assert.strictEqual(addressType, undefined);
+  }));
+});
+
+assert.doesNotThrow(() => {
+  dns.lookup('127.0.0.1', {
+    hints: 0,
+    family: 4,
+    all: false
+  }, common.mustCall((error, result, addressType) => {
+    assert.ifError(error);
+    assert.deepStrictEqual(result, '127.0.0.1');
+    assert.strictEqual(addressType, 4);
+  }));
+});
+
+assert.doesNotThrow(() => {
+  let tickValue = 0;
+
+  dns.lookup('example.com', common.mustCall((error, result, addressType) => {
+    assert(error);
+    assert.strictEqual(tickValue, 1);
+    assert.strictEqual(error.code, 'ENOENT');
+  }));
+
+  // Make sure that the error callback is called
+  // on next tick.
+  tickValue = 1;
+});