custom-config.resolver.ts

import { getSystemPath, join, Path } from '@angular-devkit/core';
import { existsSync } from 'fs';
import { Logger } from '@angular-devkit/core/src/logger';

export class CustomConfigResolver {
  constructor(private logger: Logger) {}

  resolveGlobal(workspaceRoot: Path): any {
    const packageJsonPath = getSystemPath(join(workspaceRoot, 'package.json'));
    const packageJson = require(packageJsonPath);
    const workspaceJestConfigPath = getSystemPath(join(workspaceRoot, 'jest.config.js'));

    return (
      packageJson.jest ||
      (existsSync(workspaceJestConfigPath) && require(workspaceJestConfigPath)) ||
      {}
    );
  }

  resolveForProject(projectRoot: Path, configPath: string) {
    const jestConfigPath = getSystemPath(join(projectRoot, configPath));
    if (!existsSync(jestConfigPath)) {
      this.logger.warn(
        `warning: unable to locate custom jest configuration file at path "${jestConfigPath}"`
      );
      return {};
    }
    return require(jestConfigPath);
  }
}