Node. Js: Unexpected Token {

So I have a unit test written for mocha using TypeScript. I am trying to run it using gulp (which doesn't really play a part here). I get the following exception:

(function (exports, require, module, __filename, __dirname) { import { assert } from 'chai';
                                                                     ^

SyntaxError: Unexpected token {
    at new Script (vm.js:74:7)
    at createScript (vm.js:246:10)
    at Object.runInThisContext (vm.js:298:10)
    at Module._compile (internal/modules/cjs/loader.js:657:28)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:700:10)

Could someone tell me what setting in need in my tsconfig.json to fix problems like these?

node -v 
v10.6.0
tsc -v
Version 2.9.2

and here's my tsconfig.json:

{
    "include" : [
        "src",
        "test",
        "unittest"
    ],
    "compileOnSave": true,
    "compilerOptions": {
        "module": "es2015",
        "moduleResolution": "node",
        "esModuleInterop": true,
        "target": "es5",
        "noImplicitAny": true,
        "declaration": true,
        "sourceMap": true,
        "preserveConstEnums": true,
        "lib": [
            "es2015", "dom"
        ],
        "noUnusedLocals": true,
        "noImplicitReturns": true,
        "noImplicitThis": true,
        "alwaysStrict": true,
        "strictNullChecks": false,
        "noUnusedParameters": false,
        "pretty": true,
        "allowUnreachableCode": false,
        "experimentalDecorators": true,
        "suppressImplicitAnyIndexErrors": true,
        "outDir": "./build"
    }
}