test: add tests for OutgoingMessage setTimeout

These tests ensure that OutgoingMessage setTimeout method
will call setTimeout on its socket

Co-authored-by: ZauberNerd <zaubernerd@zaubernerd.de>

PR-URL: #24148
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/parallel/test-http-outgoing-settimeout.js

@@ -0,0 +1,30 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+
+const { OutgoingMessage } = require('http');
+
+{
+  // tests for settimeout method with socket
+  const expectedMsecs = 42;
+  const outgoingMessage = new OutgoingMessage();
+  outgoingMessage.socket = {
+    setTimeout: common.mustCall((msecs) => {
+      assert.strictEqual(msecs, expectedMsecs);
+    })
+  };
+  outgoingMessage.setTimeout(expectedMsecs);
+}
+
+{
+  // tests for settimeout method without socket
+  const expectedMsecs = 23;
+  const outgoingMessage = new OutgoingMessage();
+  outgoingMessage.setTimeout(expectedMsecs);
+
+  outgoingMessage.emit('socket', {
+    setTimeout: common.mustCall((msecs) => {
+      assert.strictEqual(msecs, expectedMsecs);
+    })
+  });
+}