Basics of Jest coverage with Typescript

__tests__-campaigns.test.js

import * as jestPlugin from 'serverless-jest-plugin';
import * as mod from './../handlers/campaigns/handler';

const lambdaWrapper = jestPlugin.lambdaWrapper;
const wrapped = lambdaWrapper.wrap(mod, { handler: 'campaigns' });

describe('λ: campaigns', () => {
  beforeAll(done => {
    done();
  });

  it('GET /error', () => {
    const request = {
      isOffline: true,
      requestContext: {
        httpMethod: 'GET',
        resourcePath: '/error',
      },
    };
    return wrapped.run(request).then(response => {
      expect(response).toBeDefined();
      expect(response.body).toBeDefined();
      expect(response.statusCode).toEqual(404);
      expect(JSON.parse(response.body)).toEqual({
        Error: 'API route GET /error not found!',
      });
    });
  });
// ...

package.json

{
  "devDependencies": {
    "@types/bluebird": "^3.5.12",
    "@types/jest": "^21.1.1",
    "@types/node": "^8.0.31",
    "jest": "^21.2.0",
    "serverless-dynamodb-local": "^0.2.25",
    "serverless-jest-plugin": "^0.1.6",
    "serverless-offline": "^3.16.0",
    "serverless-plugin-typescript": "^1.1.2",
    "ts-jest": "^21.0.1",
    "ts-node": "^3.3.0",
    "tslint": "^5.7.0",
    "typescript": "^2.5.3"
  },
  "scripts": {
    "coverage": "node scripts/test --coverage --silent",
    "lint": "tslint --fix --project .",
    "prepush": "yarn coverage",
    "test": "node scripts/test"
  },
  "jest": {
    "collectCoverageFrom": [
      "handlers/**/*.ts"
    ],
    "coveragePathIgnorePatterns": [
      "<rootDir>/node_modules"
    ],
    "coverageReporters": [
      "json",
      "lcov",
      "text"
    ],
    "coverageThreshold": {
      "global": {
        "branches": 100,
        "functions": 100,
        "lines": 100,
        "statements": 100
      }
    },
    "transform": {
      ".ts": "<rootDir>/node_modules/ts-jest/preprocessor.js"
    },
    "testEnvironment": "node",
    "testRegex": "(/__tests__/.*|\\.(test|spec))\\.(ts)$",
    "moduleFileExtensions": [
      "ts",
      "js",
      "json"
    ],
    "mapCoverage": true
  }
}

scripts-test.js

// Do this as the first thing so that any code reading it knows the right env.
process.env.NODE_ENV = 'test';

// Set up AWS test settings
process.env.AWS_REGION = 'localRegion';
process.env.IS_OFFLINE = true;

// TODO: Figure out how to run DynamoDB local with test suite

// Makes the script crash on unhandled rejections instead of silently
// ignoring them. In the future, promise rejections that are not handled will
// terminate the Node.js process with a non-zero exit code.
process.on('unhandledRejection', err => {
  throw err;
});

const jest = require('jest');
const argv = process.argv.slice(2);

// Watch unless on CI or in coverage mode
if (!process.env.CI && argv.indexOf('--coverage') < 0) {
  argv.push('--watch');
}

jest.run(argv);

tsconfig.json

{
  "compilerOptions": {
    "preserveConstEnums": true,
    "strictNullChecks": true,
    "sourceMap": true,
    "declaration": true,
    "target": "es6",
    "module": "commonjs",
    "outDir": ".build",
    "typeRoots": ["node_modules/@types"],
    "lib": ["es6", "es2015"],
    "rootDir": "./"
  },
  "include": ["./database/**/*.ts", "./handlers/**/*.ts", "./__tests__/**/*.ts"],
  "exclude": ["node_modules"]
}