Angular5/Karma报错：'selector'与'dj-menu'未知元素问题求助

Hey there! I've run into this exact scenario a few times with Angular 5 and Karma—when your app works flawlessly in the browser but tests throw "unknown element" errors, it almost always boils down to your TestBed configuration not mirroring your production module setup. Let's break down how to fix both of your errors:

1. Fixing "'selector' is not a known element" #

This error means the component corresponding to that selector isn't recognized in your test module. Since your production app works, your main module is correctly set up—you just need to replicate that setup in your test's TestBed.configureTestingModule:

• If the selector belongs to a custom component you wrote, add it to the declarations array in your test config:

  import { YourComponentUnderTest } from './your-component.component';
  import { MissingComponent } from './missing-component.component';
  
  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [
        YourComponentUnderTest,
        MissingComponent // Add the component with the problematic selector here
      ]
    }).compileComponents();
  }));
  

• If the selector comes from a shared or third-party module, import that module into your test config instead:

  import { YourComponentUnderTest } from './your-component.component';
  import { SharedModuleWithTheComponent } from '../shared/shared.module';
  
  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [YourComponentUnderTest],
      imports: [SharedModuleWithTheComponent] // Import the module that declares the component
    }).compileComponents();
  }));
  

2. Fixing "'dj-menu' is not a known element" #

This error has two common fixes, matching the hints in the error message:

Case 1: 'dj-menu' is an Angular component #

Same as the first error—your test module isn't aware of the DjMenuComponent:

• If it's a custom component, add it to declarations in your TestBed config.
• If it's part of a library or module (like a custom UI library), import that module into your test's imports array.

Example code:

import { YourComponentUnderTest } from './your-component.component';
import { DjMenuModule } from '../dj-menu/dj-menu.module'; // Or the correct path

beforeEach(async(() => {
  TestBed.configureTestingModule({
    declarations: [YourComponentUnderTest],
    imports: [DjMenuModule] // Import the module containing dj-menu
  }).compileComponents();
}));

Case 2: 'dj-menu' is a Web Component (non-Angular custom element) #

If dj-menu is a third-party web component (not an Angular component), you need to tell Angular to ignore unknown elements in tests by adding CUSTOM_ELEMENTS_SCHEMA to your test config:

import { YourComponentUnderTest } from './your-component.component';
import { CUSTOM_ELEMENTS_SCHEMA } from '@angular/core';

beforeEach(async(() => {
  TestBed.configureTestingModule({
    declarations: [YourComponentUnderTest],
    schemas: [CUSTOM_ELEMENTS_SCHEMA] // Allow unknown custom elements
  }).compileComponents();
}));

Note: Make sure the web component's script is loaded before your tests run (you can add it to your karma.conf.js files array if needed).

Extra Troubleshooting Tips #

• Double-check import paths for typos—even a small spelling mistake can cause the test to fail while production works.
• If you're using lazy-loaded modules in production, your test won't automatically load them—you need to explicitly import the component/module in your TestBed config.
• For Angular 5, ensure you're importing CUSTOM_ELEMENTS_SCHEMA from @angular/core (it's supported in all Angular 2+ versions).

内容的提问来源于stack exchange，提问作者shaelex