Mocha + TypeScript: Cannot use import statement outside a module

Had the same issue and almost gave up using Mocha with TypeScript (in our case Angular 9).

This is what helped me:

In tsconfig.json:

Replaced this:

"module": "esnext", 

with this:

"module": "commonjs",

Also here I found a working example of Mocha with TypeScript and used the tsconfig file from there to compare with mine: https://medium.com/@RupaniChirag/writing-unit-tests-in-typescript-d4719b8a0a40

Also had this problem and found I didn't have to switch to commonJS, just had to enable ESM:

npm install --save-dev esm

./node_modules/mocha/bin/mocha -r esm -r ts-node/register "src/**/*Test.ts"

I was able to test thanks to the @types/chai-http – Can't use ES6 import GitHub issue's answer.

I added a second TypeScript configuration file tsconfig.testing.json with the following information:

{
    "compilerOptions": {
      "module": "commonjs",
      "target": "es2015",
      "lib": ["es2017"],
      "declaration": false,
      "noImplicitAny": false,
      "removeComments": true,
      "inlineSourceMap": true,
      "moduleResolution": "node"
    },
    "include": ["scripts/**/*.ts", "src/**/*.ts", "node_modules/lodash-es/**/*.js"]
  }

Then I changed my package.json scripts as:

"test": "env TS_NODE_PROJECT=\"tsconfig.testing.json\" mocha --require ts-node/register 'src/test/**/*.ts'",

Finally I changed the test file like:

import * as chai from 'chai';
import 'chai-http';
import server from '../app';

// Assertions
chai.should();

chai.use(require('chai-http'));

Well, running the tests works now.

Ensure you have .mocharc.json in your project:

{
  "extension": ["ts"],
  "timeout": 5000,
  "exit": true,
  "require": "ts-node/register"
}

(see also https://github.com/mochajs/mocha-examples/tree/master/packages/typescript#es-modules)