Add test for the language switcher

frontend/jest.config.js

@@ -0,0 +1,12 @@
+/** @type {import('ts-jest').JestConfigWithTsJest} **/
+export default {
+  preset: "ts-jest",
+  testEnvironment: "jsdom",
+  transform: {
+    "^.+\\.tsx?$": ["ts-jest", { tsconfig: "tsconfig.app.json" }],
+  },
+  moduleNameMapper: {
+    "\\.(css|less|scss|sss|styl)$": "<rootDir>/node_modules/jest-css-modules",
+  },
+  setupFilesAfterEnv: ["<rootDir>/jest.setup.ts"],
+};