The ultimate Node Test Runner + TypeScript + ENV variables guide

This also works in a monorepo ;)

First install dotenv-cli, tsx and glob:

# Use whatever package manager you prefer
pnpm add -D dotenv-cli tsx glob

# For a single app in a monorepo
# pnpm add -F your-app -D dotenv-cli tsx glob

# For the global package.json in a monorepo
# pnpm add -wD dotenv-cli tsx glob

Assuming you want environment variable control, create a .env and a .env.test at the root of the app you want to configure (optional, since dotenv-cli doesn't throw an error if they don't exist).

Add this to your app's package.json:

"scripts": {
    //...
    "test": "dotenv -e .env -e env.test -- glob -c \"tsx --test --test-reporter spec \" \"./test/**/*.test.ts\"",
    "build": "tsc -p tsconfig.build.json",

What that test script does is load your .env and .env.test files (the latter overwrites the first in case of conflict), then asks glob to process the "./test/**/*.test.ts\" (which will load all Typescript files in the ./test folder ending in .test.ts) and runs the tests via tsx and with a more human-readable output (--test-reporter spec). This last step is equivalent to node --import tsx --test.

Finally, adapt your tsconfig.json to include your tests if you want decent imports, linting and others (in my case I had to split my tsconfig into 2: tsconfig.json and tsconfig.build.json, both in the root folder of the app):

// tsconfig.json
{
    "extends": "../../tsconfig.json", // Since I work in a monorepo, this one contains all generic compiler options. You can write them in this file if you prefer
    "compilerOptions": { // These are for shorter, non-relative imports in tests. Completely optional
        "baseUrl": "./",
        "paths": {
            "@src/*": ["./src/*"], 
        },
        "noEmit": true, // Avoid compiling by mistake
    },
    "include": ["./src/**/*", "./test/**/*"], // Important so tests also benefit from TS support
}

// tsconfig.build.json
{
    "extends": "./tsconfig.json", // The file above. You can also just extend the base `tsconfig.json` (in the root of the monorepo) instead, adding `include: [ "./src/**/*"]`, or write the `compilerOptions` here
    "compilerOptions": {
        "noEmit": false,
        "outDir": "./dist",
    },
    "exclude": [ // This way we avoid compiling tests into JS
        "**/*.spec.ts",
        "**/*.test.ts"
    ]
}

And that should be it, really. Hope it is of help when setting up your TypeScript testing environment!

For more information, check this GitHub issue.

I also made a GitHub Gist to go along with this guide