test: imporove assert messages

Improve assert messages in test-cluster-worker-disconnect.js.

PR-URL: #16021
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

test/parallel/test-cluster-worker-disconnect.js

@@ -41,7 +41,7 @@ if (cluster.isWorker) {
   // Disconnect worker when it is ready
   worker.once('listening', common.mustCall(() => {
     const w = worker.disconnect();
-    assert.strictEqual(worker, w, 'did not return a reference');
+    assert.strictEqual(worker, w, `${worker.id} did not return a reference`);
   }));
 
   // Check cluster events
@@ -80,10 +80,8 @@ if (cluster.isWorker) {
     assert.ok(c.emitExit, 'Exit event did not emit');
 
     // flags
-    assert.strictEqual(w.state, 'disconnected',
-                       'The state property was not set');
-    assert.strictEqual(w.voluntaryMode, true,
-                       'Voluntary exit mode was not set');
+    assert.strictEqual(w.state, 'disconnected');
+    assert.strictEqual(w.voluntaryMode, true);
 
     // is process alive
     assert.ok(w.died, 'The worker did not die');