diff --git a/test/file/test_plugin/control.js b/test/file/test_plugin/control.js
new file mode 100644
index 00000000..25a80a0c
--- /dev/null
+++ b/test/file/test_plugin/control.js
@@ -0,0 +1,26 @@
+"use strict";
+const { Command, CommandTree } = require("@clusterio/lib");
+const { BaseCtlPlugin } = require("@clusterio/ctl");
+
+const testPluginCommands = new CommandTree({
+	name: "test-plugin", description: "Test plugin commands",
+});
+testPluginCommands.add(new Command({
+	definition: ["echo <message>", "Print the message given to it", (yargs) => {
+		yargs.positional("message", { describe: "message to print", type: "string" });
+	}],
+	handler: async function(args, control) {
+		// eslint-disable-next-line no-console
+		console.log(args.message);
+	},
+}));
+
+class CtlPlugin extends BaseCtlPlugin {
+	async addCommands(rootCommand) {
+		rootCommand.add(testPluginCommands);
+	}
+}
+
+module.exports = {
+	CtlPlugin,
+};
diff --git a/test/file/test_plugin/controller.js b/test/file/test_plugin/controller.js
new file mode 100644
index 00000000..01988f39
--- /dev/null
+++ b/test/file/test_plugin/controller.js
@@ -0,0 +1,21 @@
+"use strict";
+const { BaseControllerPlugin } = require("@clusterio/controller");
+
+const { ControllerEcho, HostEcho } = require("./messages");
+
+class ControllerPlugin extends BaseControllerPlugin {
+	async init() {
+		this.logger.info("test_plugin controller loaded");
+		this.controller.handle(ControllerEcho, this.handleControllerEcho.bind(this));
+	}
+
+	async handleControllerEcho(request) {
+		this.logger.info(`test_plugin controller echo ${request.text}`);
+		this.broadcastEventToHosts(new HostEcho(request.text));
+		return request.text;
+	}
+}
+
+module.exports = {
+	ControllerPlugin,
+};
diff --git a/test/file/test_plugin/host.js b/test/file/test_plugin/host.js
new file mode 100644
index 00000000..ca6a3bad
--- /dev/null
+++ b/test/file/test_plugin/host.js
@@ -0,0 +1,26 @@
+"use strict";
+const { BaseHostPlugin } = require("@clusterio/host");
+
+const { HostEcho, HostEchoReceived } = require("./messages");
+
+class HostPlugin extends BaseHostPlugin {
+	async init() {
+		this.logger.info("test_plugin host loaded");
+		this.receivedEchoes = new Set();
+		this.host.handle(HostEcho, this.handleHostEcho.bind(this));
+		this.host.handle(HostEchoReceived, this.handleHostEchoReceived.bind(this));
+	}
+
+	async handleHostEcho(event) {
+		this.logger.info(`test_plugin host echo ${event.text}`);
+		this.receivedEchoes.add(event.text);
+	}
+
+	async handleHostEchoReceived(request) {
+		return this.receivedEchoes.has(request.text);
+	}
+}
+
+module.exports = {
+	HostPlugin,
+};
diff --git a/test/file/test_plugin/index.js b/test/file/test_plugin/index.js
new file mode 100644
index 00000000..7938c45b
--- /dev/null
+++ b/test/file/test_plugin/index.js
@@ -0,0 +1,24 @@
+"use strict";
+// Plugin exercising the plugin system in the integration tests, see #342.
+// Written as plain JavaScript so that it does not need to be built.
+
+const { ControllerEcho, HostEcho, HostEchoReceived } = require("./messages");
+
+module.exports = {
+	plugin: {
+		name: "test_plugin",
+		title: "Test Plugin",
+		description: "Plugin used to test the plugin system.",
+
+		controllerEntrypoint: "controller",
+		hostEntrypoint: "host",
+		instanceEntrypoint: "instance",
+		ctlEntrypoint: "control",
+
+		messages: [
+			ControllerEcho,
+			HostEcho,
+			HostEchoReceived,
+		],
+	},
+};
diff --git a/test/file/test_plugin/instance.js b/test/file/test_plugin/instance.js
new file mode 100644
index 00000000..5296c026
--- /dev/null
+++ b/test/file/test_plugin/instance.js
@@ -0,0 +1,12 @@
+"use strict";
+const { BaseInstancePlugin } = require("@clusterio/host");
+
+class InstancePlugin extends BaseInstancePlugin {
+	async init() {
+		this.logger.info("test_plugin instance loaded");
+	}
+}
+
+module.exports = {
+	InstancePlugin,
+};
diff --git a/test/file/test_plugin/messages.js b/test/file/test_plugin/messages.js
new file mode 100644
index 00000000..be98c2c4
--- /dev/null
+++ b/test/file/test_plugin/messages.js
@@ -0,0 +1,63 @@
+"use strict";
+const { JsonBoolean, JsonString } = require("@clusterio/lib");
+
+// Sent from ctl to the controller, which answers with the text it was given
+// and broadcasts a HostEcho to the hosts.
+class ControllerEcho {
+	static type = "request";
+	static src = "control";
+	static dst = "controller";
+	static plugin = "test_plugin";
+	static permission = null;
+	static Response = JsonString;
+
+	constructor(text) {
+		this.text = text;
+	}
+
+	static jsonSchema = { type: "string" };
+	toJSON() { return this.text; }
+	static fromJSON(json) { return new this(json); }
+}
+
+// Broadcast from the controller to the hosts by broadcastEventToHosts.
+class HostEcho {
+	static type = "event";
+	static src = "controller";
+	static dst = "host";
+	static plugin = "test_plugin";
+	static permission = null;
+
+	constructor(text) {
+		this.text = text;
+	}
+
+	static jsonSchema = { type: "string" };
+	toJSON() { return this.text; }
+	static fromJSON(json) { return new this(json); }
+}
+
+// Sent from ctl to a host, which answers with whether it received the given
+// text via a HostEcho.
+class HostEchoReceived {
+	static type = "request";
+	static src = "control";
+	static dst = "host";
+	static plugin = "test_plugin";
+	static permission = null;
+	static Response = JsonBoolean;
+
+	constructor(text) {
+		this.text = text;
+	}
+
+	static jsonSchema = { type: "string" };
+	toJSON() { return this.text; }
+	static fromJSON(json) { return new this(json); }
+}
+
+module.exports = {
+	ControllerEcho,
+	HostEcho,
+	HostEchoReceived,
+};
diff --git a/test/file/test_plugin/package.json b/test/file/test_plugin/package.json
new file mode 100644
index 00000000..16079ed7
--- /dev/null
+++ b/test/file/test_plugin/package.json
@@ -0,0 +1,10 @@
+{
+	"name": "test_plugin",
+	"version": "0.0.1",
+	"description": "Plugin used to test the plugin system, see #342",
+	"private": true,
+	"main": "index.js",
+	"keywords": [
+		"clusterio-plugin"
+	]
+}
diff --git a/test/integration/clusterio.js b/test/integration/clusterio.js
index 2729eb8a..780a4dcc 100644
--- a/test/integration/clusterio.js
+++ b/test/integration/clusterio.js
@@ -16,6 +16,7 @@ const {
 	spawnNode, instancesDir, factorioDir, databaseDir, controllerConfigPath,
 	requiresFactorio, hasFactorio,
 } = require("./index");
+const { ControllerEcho, HostEchoReceived } = require("../file/test_plugin/messages");
 
 
 /** @returns {Promise<Map<number, lib.InstanceDetails>>} */
@@ -386,6 +387,64 @@ describe("Integration of Clusterio", function() {
 		});
 	});
 
+	describe("plugin system", function() {
+		// Exercised with test/file/test_plugin, which is a plugin that exists
+		// only to be loaded by these tests, see #342.
+		async function pluginDetails(address) {
+			const plugins = await getControl().sendTo(address, new lib.PluginListRequest());
+			const details = plugins.find(plugin => plugin.name === "test_plugin");
+			assert(details, `test_plugin missing from the plugin list of ${JSON.stringify(address)}`);
+			return details;
+		}
+
+		it("should load the plugin on the controller", async function() {
+			const details = await pluginDetails("controller");
+			assert(details.enabled, "test_plugin is not enabled on the controller");
+			assert(details.loaded, "test_plugin is not loaded on the controller");
+		});
+
+		it("should load the plugin on the host", async function() {
+			const details = await pluginDetails({ hostId: 4 });
+			assert(details.enabled, "test_plugin is not enabled on the host");
+			assert(details.loaded, "test_plugin is not loaded on the host");
+		});
+
+		it("should report the plugin's title and version", async function() {
+			const details = await pluginDetails("controller");
+			assert.equal(details.title, "Test Plugin");
+			assert.equal(details.version, "0.0.1");
+		});
+
+		it("should add the plugin's command to clusterioctl", async function() {
+			const { stdout } = await execCtlProcess("test-plugin echo works");
+			assert(stdout.includes("works"), `plugin command did not print its message, got ${stdout}`);
+		});
+
+		it("should route a plugin request from control to the controller", async function() {
+			const response = await getControl().sendTo("controller", new ControllerEcho("to-controller"));
+			assert.equal(response, "to-controller");
+		});
+
+		it("should route a plugin request from control to a host", async function() {
+			const received = await getControl().sendTo({ hostId: 4 }, new HostEchoReceived("never-broadcast"));
+			assert.equal(received, false);
+		});
+
+		it("should deliver a plugin event sent with broadcastEventToHosts", async function() {
+			await getControl().sendTo("controller", new ControllerEcho("to-hosts"));
+
+			// The broadcast is sent without waiting for the hosts to receive it.
+			let received = false;
+			for (let attempt = 0; attempt < 100 && !received; attempt++) {
+				received = await getControl().sendTo({ hostId: 4 }, new HostEchoReceived("to-hosts"));
+				if (!received) {
+					await lib.wait(20);
+				}
+			}
+			assert(received, "host did not receive the event broadcast to it");
+		});
+	});
+
 	describe("clusterioctl", function() {
 		describe("controller config list", function() {
 			it("runs", async function() {
diff --git a/test/integration/index.js b/test/integration/index.js
index 4a529471..1dbf56c3 100644
--- a/test/integration/index.js
+++ b/test/integration/index.js
@@ -350,6 +350,7 @@ before(async function() {
 	await execController("config set controller.tls_private_key ../../test/file/tls/key.pem");
 
 	console.log("Setting Controller Plugins");
+	await execCtlProcess("plugin add ../../test/file/test_plugin");
 	await execCtlProcess("plugin add ../../plugins/global_chat");
 	await execCtlProcess("plugin add ../../plugins/research_sync");
 	await execCtlProcess("plugin add ../../plugins/statistics_exporter");