socket-mode: do not throw exception when calling disconnect() and alr…

…eady disconnected; do not raise slack_event in case of type:disconnect messages (#1762) also add integration tests to this maintenance branch

packages/socket-mode/apptest.ts

@@ -0,0 +1,10 @@
+const { SocketModeClient, LogLevel } = require('./dist');
+const client = new SocketModeClient({ appToken: process.env.SLACK_APP_TOKEN, logLevel: LogLevel.DEBUG });
+
+client.on('message', async (evt) => {
+  await evt.ack();
+  console.log('*MESSAGE EVENT*', evt);
+});
+(async () => {
+  await client.start();
+})();