tools: use no-useless-concat ESLint rule

* Add `no-useless-concat: error` to .eslintrc.yaml.
* Apply no-useless-concat rule to tests.

PR-URL: https://github.com/nodejs/node/pull/12613
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Teddy Katz <teddy.katz@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>

1 files changed, 2 insertions, 2 deletions

diff --git a/test/parallel/test-net-write-connect-write.js b/test/parallel/test-net-write-connect-write.js
index a403691ded..1f09b04f17 100644
--- a/test/parallel/test-net-write-connect-write.js
+++ b/test/parallel/test-net-write-connect-write.js
@@ -33,7 +33,7 @@ const server = net.createServer(function(socket) {
   conn.setEncoding('utf8');
   conn.write('before');
   conn.on('connect', function() {
-    conn.write('after');
+    conn.write(' after');
   });
   conn.on('data', function(buf) {
     received += buf;
@@ -41,6 +41,6 @@ const server = net.createServer(function(socket) {
   });
   conn.on('end', common.mustCall(function() {
     server.close();
-    assert.strictEqual(received, 'before' + 'after');
+    assert.strictEqual(received, 'before after');
   }));
 }));