@stryker-mutator/karma-runner/src/karma-plugins/test-hooks-middleware.ts

A plugin to use the karma test runner in Stryker, the JavaScript mutation testing framework

import path from 'path';
import url, { fileURLToPath } from 'url';

import { RequestHandler } from 'express';
import {
  CoverageAnalysis,
  INSTRUMENTER_CONSTANTS,
} from '@stryker-mutator/api/core';
import { MutantRunOptions } from '@stryker-mutator/api/test-runner';
import { escapeRegExpLiteral } from '@stryker-mutator/util';

export const TEST_HOOKS_FILE_NAME = path.resolve(
  path.dirname(fileURLToPath(import.meta.url)),
  'test-hooks-middleware-21f23d35-a4c9-4b01-aeff-da9c99c3ffc0.js',
);
const TEST_HOOKS_FILE_BASE_NAME = path.basename(TEST_HOOKS_FILE_NAME);

const SUPPORTED_FRAMEWORKS = Object.freeze(['mocha', 'jasmine'] as const);

type SupportedFramework = 'jasmine' | 'mocha';

function isSupportedFramework(
  framework: string,
): framework is SupportedFramework {
  return (SUPPORTED_FRAMEWORKS as readonly string[]).includes(framework);
}

/**
 * Keep in sync with StrykerMutantCoverageAdapter.ts
 */
const SHOULD_REPORT_COVERAGE_FLAG = '__strykerShouldReportCoverage__';

const { ACTIVE_MUTANT, NAMESPACE, CURRENT_TEST_ID, HIT_COUNT, HIT_LIMIT } =
  INSTRUMENTER_CONSTANTS;

export class TestHooksMiddleware {
  private static _instance?: TestHooksMiddleware;
  private testFramework: 'jasmine' | 'mocha' | undefined;
  public currentTestHooks = '';

  public static get instance(): TestHooksMiddleware {
    if (!this._instance) {
      this._instance = new TestHooksMiddleware();
    }
    return this._instance;
  }

  public configureTestFramework(frameworks?: string[]): void {
    this.testFramework = frameworks?.find(isSupportedFramework);
  }

  public configureCoverageAnalysis(coverageAnalysis: CoverageAnalysis): void {
    switch (coverageAnalysis) {
      case 'perTest':
        this.configurePerTestCoverageAnalysis();
        break;
      case 'all':
        this.currentTestHooks = `window.${SHOULD_REPORT_COVERAGE_FLAG} = true;`;
        break;
      case 'off':
        this.currentTestHooks = `window.${SHOULD_REPORT_COVERAGE_FLAG} = false;`;
        break;
    }
  }

  public configureMutantRun({
    activeMutant,
    testFilter,
    hitLimit,
  }: MutantRunOptions): void {
    this.configureCoverageAnalysis('off');
    this.currentTestHooks += `window.${NAMESPACE} = window.${NAMESPACE} || {};`;
    this.currentTestHooks += this.configureHitLimit(hitLimit);
    this.currentTestHooks += `window.${NAMESPACE}.${ACTIVE_MUTANT} = "${activeMutant.id}";`;
    if (testFilter) {
      switch (this.testFramework) {
        case 'jasmine':
          this.currentTestHooks += `jasmine.getEnv().configure({ specFilter: function(spec) {
            return ${JSON.stringify(testFilter)}.indexOf(spec.id) !== -1;
          }})`;
          break;
        case 'mocha': {
          const metaRegExp = testFilter
            .map((testId) => `(${escapeRegExpLiteral(testId)})`)
            .join('|');
          this.currentTestHooks += `mocha.grep(/${metaRegExp}/)`;
          break;
        }
        default:
      }
    }
  }

  private configureHitLimit(hitLimit: number | undefined) {
    return `window.${NAMESPACE}.${HIT_COUNT} = ${hitLimit === undefined ? undefined : 0};
    window.${NAMESPACE}.${HIT_LIMIT} = ${hitLimit};`;
  }

  private configurePerTestCoverageAnalysis() {
    this.currentTestHooks = ` 
    window.${SHOULD_REPORT_COVERAGE_FLAG} = true;
    window.${NAMESPACE} = window.${NAMESPACE} || {};`;
    switch (this.testFramework) {
      case 'jasmine':
        this.currentTestHooks += `
      jasmine.getEnv().addReporter({
        specStarted: function (spec) {
          window.${NAMESPACE}.${CURRENT_TEST_ID} = spec.id;
        }
      });`;
        break;
      case 'mocha':
        this.currentTestHooks += `
        beforeEach(function() {
          window.${NAMESPACE}.${CURRENT_TEST_ID} = this.currentTest && this.currentTest.fullTitle();
        });
      `;
        break;
      case undefined:
        throw new Error(
          `Could not configure coverageAnalysis "perTest". Your test framework is not supported by the \`@stryker-mutator/karma-runner\`. Supported test frameworks: ${SUPPORTED_FRAMEWORKS.join(
            ', ',
          )}.`,
        );
    }
  }

  public handler: RequestHandler = (request, response, next) => {
    const pathName = url.parse(request.url).pathname;
    if (pathName?.endsWith(TEST_HOOKS_FILE_BASE_NAME)) {
      response.writeHead(200, {
        'Cache-Control': 'no-cache',
        'Content-Type': 'application/javascript',
      });
      response.end(this.currentTestHooks);
    } else {
      next();
    }
  };
}