Jest typescript tests runs twice, one for ts files, and one for js files

Is this normal in ts-jest or am I missing some extra configuration

You should set roots to /src only. Here is a good config:

module.exports = {
  "roots": [
    "<rootDir>/src"
  ],
  "transform": {
    "^.+\\.tsx?$": "ts-jest"
  },
  "testRegex": "(/__tests__/.*|(\\.|/)(test|spec))\\.tsx?$",
  "moduleFileExtensions": [
    "ts",
    "tsx",
    "json"
  ],
}

I also only test .tsx? files (no .jsx?) ;)

Had the same issue, using the aws cdk in Typescript, to prevent it, I added .js to the testPathIgnorePatterns property in jest-config.js

module.exports = {
  preset: 'ts-jest',
  testEnvironment: 'node',
  testPathIgnorePatterns: [".d.ts", ".js"]
};