TypeScript + Jest環境構築例

install.sh

yarn add -D \
  typescript \
  jest \
  ts-jest \
  @types/jest

jest.config.js

module.exports = {
  moduleFileExtensions: ["js", "ts"],
  moduleNameMapper: {
    "^~/(.*)$": "<rootDir>/src/$1",
  },
  transform: {
    "^.+\\.ts$": "ts-jest",
  },
  globals: {
    "ts-jest": { tsConfig: "<rootDir>/tsconfig.json" },
  },
  testMatch: ["<rootDir>/tests/**/*.spec.{js,ts}"],
  collectCoverage: true,
  collectCoverageFrom: ["<rootDir>/src/**/*.{js,ts}"]
}

package.json

{
  "scripts": {
    "test": "jest"
  },
  "devDependencies": {
    "@types/jest": "^25.2.1",
    "jest": "^25.4.0",
    "ts-jest": "^25.4.0",
    "typescript": "^3.8.3"
  }
}

tsconfig.json

{
  "compilerOptions": {
    "baseUrl": "./src",
    "paths": { "~/*": ["*"] },
    "types": ["@types/jest"]
  }
}