dns: Add setServers into 'dns/promises'

lib/dns/promises.js

@@ -1,3 +1,5 @@
 'use strict';
 
-module.exports = require('internal/dns/promises');
+const dnsPromises = require('internal/dns/promises');
+dnsPromises.setServers = require('dns').setServers;
+module.exports = dnsPromises;

test/parallel/test-dns-setservers-type-check.js

@@ -85,3 +85,38 @@ const promiseResolver = new dns.promises.Resolver();
     );
   });
 }
+
+// This test for 'dns/promises'
+{
+  const {
+    setServers,
+    resolve
+  } = require('dns/promises');
+
+  // This should not throw any error.
+  (async () => {
+    const localhost = await resolve('localhost');
+    setServers(localhost);
+  })();
+
+  [
+    [null],
+    [undefined],
+    [Number(addresses.DNS4_SERVER)],
+    [
+      {
+        address: addresses.DNS4_SERVER
+      }
+    ]
+  ].forEach((val) => {
+    const errObj = {
+      code: 'ERR_INVALID_ARG_TYPE',
+      name: 'TypeError',
+      message: 'The "servers[0]" argument must be of type string.' +
+              common.invalidArgTypeHelper(val[0])
+    };
+    assert.throws(() => {
+      setServers(val);
+    }, errObj);
+  });
+}