Install JMeter https://jmeter.apache.org/download_jmeter.cgi and Java 8+

Install JMeter Plugin for installing other plugins https://jmeter-plugins.org/install/Install/ place jar file in JMeter lib/ext.

Restart JMeter and goto menu Options -> Plugin Manager

Search GCP pubsub plugin check and click Apply Changes and Restart JMeter

Download dependencies for the plugin and place the jar file in the JMeter lib directory. google-cloud-pubsub and gson

Add Config sections PubSub-PublisherConfiguration or PubSub-PublisherConfiguration with service account credential to test plan.

Add sampler Publisher Request or Subscriber Request to the thread group with the data you want to test.

Run load test scenarios as planned.