fixes #5259

src/vs/workbench/electron-main/main.ts

@@ -212,17 +212,18 @@ function setupIPC(): TPromise<Server> {
 				app.dock.hide();
 			}
 
-			// Tests from CLI require to be the only instance currently (TODO@Ben support multiple instances and output)
-			if (env.isTestingFromCli) {
-				const errorMsg = 'Running extension tests from the command line is currently only supported if no other instance of Code is running.';
-				console.error(errorMsg);
-
-				return TPromise.wrapError(errorMsg);
-			}
-
 			// there's a running instance, let's connect to it
 			return connect(env.mainIPCHandle).then(
 				client => {
+
+					// Tests from CLI require to be the only instance currently (TODO@Ben support multiple instances and output)
+					if (env.isTestingFromCli) {
+						const msg = 'Running extension tests from the command line is currently only supported if no other instance of Code is running.';
+						console.error(msg);
+						client.dispose();
+						return TPromise.wrapError(msg);
+					}
+
 					env.log('Sending env to running instance...');
 
 					const service = client.getService<LaunchService>('LaunchService', LaunchService);