Add testing setup

Author: faassen

.eslintignore

@@ -1,3 +1,4 @@
 .eslintrc.js
 dist
 webpack.*.js
+jest.config.js

backend/message.test.ts

@@ -0,0 +1,3 @@
+test("hello", () => {
+  expect(0).toBe(0);
+});

jest.config.js

@@ -0,0 +1,11 @@
+module.exports = {
+  testEnvironment: "node",
+  testMatch: [
+    "<rootDir>/backend/**/__tests__/**/*.{ts,tsx}",
+    "<rootDir>/backend/**/?(*.)(test).{ts,tsx}",
+  ],
+  // SWC instead of ts-jest
+  transform: {
+    "^.+\\.(t|j)sx?$": ["@swc/jest"],
+  },
+};