Angular 9配置Jest（jest-preset-angular v9）遇ngModule空值错误

在Angular 9项目中配置Jest，使用v9版本的jest-preset-angular，测试代码可运行但抛出TypeError: Cannot read property 'ngModule' of null错误，以下是当前配置和测试代码，及调试解决步骤：

当前 jest.config.json 配置 #

{"preset": "jest-preset-angular",
"setupFilesAfterEnv": [
    "<rootDir>/setup-jest.ts"
],
"transformIgnorePatterns": [
    "node_modules/(?!@ngrx|ngx-socket-io)" 
],
"transform": {
    "^.+\\.(ts|js|html)$": "ts-jest"
},
"testPathIgnorePatterns": [
    "<rootDir>/node_modules/",
    "<rootDir>/dist/",
    "<rootDir>/src/test.ts"
],
"modulePaths": ["<rootDir>"]}

测试文件代码 #

import { async, ComponentFixture, TestBed } from '@angular/core/testing';
import { myComponent } from './knowuser.component';

import 'zone.js';
import 'zone.js/dist/async-test.js';
import 'zone.js/dist/proxy.js';
import 'zone.js/dist/zone-testing';

describe('myComponent', () => {
  let component: myComponent;
  let fixture: ComponentFixture<myComponent>;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [ myComponent ]
    })
    .compileComponents();
  }));

  beforeEach(() => {
    fixture = TestBed.createComponent(myComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  });

  it('should create', () => {
    expect(component).toBeTruthy();
  });
});

调试解决步骤 #

• 检查setup-jest.ts配置
  确保setup-jest.ts中正确导入jest-preset-angular的初始化代码，内容需包含：

  import 'jest-preset-angular';
  

  该文件缺失或配置错误是此类ngModule报错的常见原因。

• 移除测试文件中的zone.js重复导入
  jest-preset-angular已自动配置zone-testing环境，手动导入的zone.js模块会和预设冲突，直接删除以下导入行：

  import 'zone.js';
  import 'zone.js/dist/async-test.js';
  import 'zone.js/dist/proxy.js';
  import 'zone.js/dist/zone-testing';
  

• 调整jest的transform规则
  使用jest-preset-angular自带的转换器替代手动配置的ts-jest，避免版本兼容问题，修改transform字段：

  "transform": {
    "^.+\\.(ts|js|html)$": "jest-preset-angular"
  }
  

• 补全组件依赖配置
  如果myComponent依赖其他模块、服务或指令，需在TestBed.configureTestingModule中添加对应声明/导入：

  TestBed.configureTestingModule({
    declarations: [ myComponent, 依赖的管道/指令 ],
    imports: [ 依赖的模块 ],
    providers: [ 依赖的服务 ]
  })
  

• 清除Jest缓存
  执行命令清除缓存，避免旧缓存引发异常：

  npx jest --clearCache
  

内容的提问来源于stack exchange，提问作者TheViralGriffin