Running tests located in a separate directory with mocha and ts-node?

Question

I have source code and tests separated as follows:

`src/main/ts/hello.ts`  //SOURCE FILES HERE
`src/test/ts/hello.spec.ts` //SPEC FILES HERE

The import statement in src/test/ts/hello.spec.ts looks like this:

import hello from 'hello';

The hello.ts source code looks like this:

    export function hello() {
      return 'Hello World!';
    }

    export default hello;

My tsconfig.json is setup such that the test files can import source modules without using relative paths like this:

    {
       "include": [
         "src/main/ts/**/*.ts"
       ],
       "exclude": [
         "node_modules"
       ],

       "compilerOptions": {
         "experimentalDecorators": true,
         "noImplicitAny": true,
         "moduleResolution": "node",
         "target": "es6",
         "baseUrl": ".",
         "paths": {
           "*": [
             "*", "src/main/ts/*"
           ]
         }
       }
     }

This way the hello.spec.ts file can import hello using the statement import hello from 'hello';

I'm trying to run the tests with npm test configured to run mocha and tsnode like this (Based on this article ):

"scripts": {
  "test": "mocha -r ts-node/register src/test/ts"
},

However it does not look like ts-node is picking up on my tsconfig.json configuration as I get this error:

mocha -r ts-node/register src/test/ts

Error: Cannot find module 'hello'
    at Function.Module._resolveFilename (module.js:336:15)
    at Function.Module._load (module.js:286:25)

Answer 1

The module resolution that you set through paths in tsconfig.json is purely an compile-time thing . (See this ts-node issue report and this TypeScript issue report for details.) It does not affect how the code is emitted, which means that your test file is doing a require("hello") , which Node cannot resolve. The consequence of paths being a compile-time thing is that your module loader needs to be configured to also perform the same kind of resolution that you specify in tsconfig.json . If you were using RequireJS, for instance, you'd need to have a configuration for it that does the same thing paths in tsconfig.json does. You are using Node, however...

What you can do in Node is use tsconfig-paths , which will read the tsconfig.json , parse the paths setting and change the module resolution in Node so that it works.

Using your code, I modified hello.spec.ts to have at least one test for feedback:

import hello from "hello";
import "mocha";

it("q", () => {
    if (hello() !== "Hello World!") {
        throw new Error("unequal");
    }
});

I installed tsconfig-paths and @types/mocha (so that import "mocha" does the right thing compilation-wise in the test file I show above) and invoked Mocha like this:

$ ./node_modules/.bin/mocha --compilers ts:ts-node/register -r tsconfig-paths/register 'src/test/ts/**/*.ts'

I got this output:

  ✓ q

  1 passing (20ms)