added jest for tests

backend/jest.config.js

@@ -0,0 +1,18 @@
+/** @type {import('ts-jest').JestConfigWithTsJest} */
+module.exports = {
+  preset: 'ts-jest',
+  testEnvironment: 'node',
+  roots: ['<rootDir>/src'],
+  testMatch: [
+    '**/__tests__/**/*.+(ts|tsx|js)',
+    '**/?(*.)+(spec|test).+(ts|tsx|js)'
+  ],
+  transform: {
+    '^.+\.(ts|tsx)$': 'ts-jest',
+  },
+  collectCoverageFrom: [
+    'src/**/*.{js,ts}',
+    '!src/server.ts',
+    '!src/**/*.d.ts'
+  ],
+};