Add jest config and test environment to launch app

jest.config.js

@@ -0,0 +1,7 @@
+module.exports = {
+	globals: {
+		__APP__: undefined, // A different app will be launched in each test environment
+	},
+	testEnvironment: "./tests/environment",
+	testTimeout: 30000, // 30s
+};

tests/environment.js

@@ -0,0 +1,45 @@
+const path = require("path");
+
+const getPort = require("get-port");
+const NodeEnvironment = require("jest-environment-node");
+const { Application } = require("spectron");
+
+class TestEnvironment extends NodeEnvironment {
+	constructor(config) {
+		super(config);
+	}
+
+	async setup() {
+		await super.setup();
+
+		const electronPath = path.resolve(
+			__dirname,
+			"..",
+			"node_modules",
+			".bin",
+			"electron"
+		);
+		const appPath = path.resolve(__dirname, "..");
+		const port = await getPort();
+
+		this.global.__APP__ = new Application({
+			path: electronPath,
+			args: [appPath],
+			port,
+		});
+		await this.global.__APP__.start();
+		const { client } = this.global.__APP__;
+		await client.waitUntilWindowLoaded();
+	}
+
+	async teardown() {
+		await this.global.__APP__.stop();
+		await super.teardown();
+	}
+
+	runScript(script) {
+		return super.runScript(script);
+	}
+}
+
+module.exports = TestEnvironment;