Cannot find name 'it' in Jest TypeScript

For me, the problem was that my tsconfig.json was built with

  "include": [
    "src"
  ]

I had to change that to

  "include": [
    "src",
    "tests"
  ]

(My tests all being in directory 'tests')

Install

npm install -D jest @types/jest ts-jest

jest.config.js -- at root

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

tsconfig.json

{
    "compilerOptions": {
     ...

      "types": ["reflect-metadata", "jest"],
      "typeRoots": ["./types", "./node_modules/@types"]
     
     ...
    },
    "exclude": ["node_modules", "**/*.spec.ts", "**/*.test.ts"],
    "include": ["./src/**/*.tsx", "./src/**/*.ts"]
  }

In tsconfig.json add the below code

"types": ["jest"],
"typeRoots": ["./src/types", "node_modules/@types"],