demo.spec.ts

/// <reference types="cypress"/>
import createEmptyDb from '../../../back-end/test/create-empty-db'

describe('Demo test', () => {
  before(async () => {
    await createEmptyDb()
  })

  ...
})

plugins__index.js

// ***********************************************************
// This example plugins/index.js can be used to load plugins
//
// You can change the location of this file or turn off loading
// the plugins file with the 'pluginsFile' configuration option.
//
// You can read more here:
// https://on.cypress.io/plugins-guide
// ***********************************************************

// This function is called when a project is opened or re-opened (e.g. due to
// the project's config changing)

const path = require('path')
const wp = require('@cypress/webpack-preprocessor')
const nodeExternals = require('webpack-node-externals')

module.exports = (on) => {
  const options = {
    webpackOptions: {
      resolve: {
        extensions: ['.ts', '.tsx', '.mjs', '.js']
      },
      externals: {
        // Possible drivers for knex - we'll ignore them
        'knex': 'commonjs knex',
        'child_process': 'child_process',
        'fs': 'fs',
        'dns': 'dns',
        'net': 'net',
        'pg-native': 'pg-native',
        'tls': 'tls'
      },
      module: {
        rules: [
          {
            test: /\.tsx?$/,
            loader: 'ts-loader',
            options: { transpileOnly: true }
          }
        ]
      }
    }
  }
  on('file:preprocessor', wp(options))
}

tsconfig.json

{
  "compilerOptions": {
    "target": "esnext",
    "lib": ["esnext", "esnext.asynciterable", "dom"],
    "outDir": "dist",
    "module": "commonjs",
    "moduleResolution": "node",
    "esModuleInterop": true,
    "allowSyntheticDefaultImports": true,
    "sourceMap": true,
    "noImplicitAny": false,
    "strict": false,
    "inlineSources": true,
    "types": ["node", "jest"],
    "forceConsistentCasingInFileNames": true,
    "suppressImplicitAnyIndexErrors": true,
    "noUnusedLocals": true,
    "resolveJsonModule": true,
    "noUnusedParameters": true,
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "strictPropertyInitialization": false,
    "allowUnreachableCode": false,
    "allowJs": true,
    "jsx": "react",
    "preserveConstEnums": true,
    "skipLibCheck": true
  },
  "exclude": [
    ".git",
    "**/*.spec.js",
    "**/node_modules/**",
    "**/dist/**",
    "**/build/**",
    "./node_modules/*"
  ]
}

Getting this error: