要在测试中覆盖ModalController提供程序，请执行以下操作：

it('close closes the dialog', async () => {
  // Override the ModalController provider for the TestDialogComponent component
  TestBed.overrideComponent(TestDialogComponent, {
    providers: [
      {
        provide: ModalController,
        useValue: {
          dismiss: () => Promise.resolve()
        }
      }
    ]
  });

  // Create a fixture for the TestDialogComponent component
  const fixture = TestBed.createComponent(TestDialogComponent);
  const component = fixture.componentInstance;

  // Call the close method on the component
  await component.close();

  // Expect the dismiss method on the mock ModalController to have been called
  expect(spyOn(TestBed.inject(ModalController), 'dismiss')).toHaveBeenCalled();
});

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我找到了以下解决方案。但我不明白为什么我需要在这种情况下，在其他情况下，覆盖的提供程序的工作...

import { ComponentFixture, TestBed } from '@angular/core/testing';
import { IonicModule, ModalController } from '@ionic/angular';
import { BrowserModule } from '@angular/platform-browser';
import { Component } from '@angular/core';

@Component({
    selector: 'app-test-dialog',
    template: '',
    imports: [
        IonicModule
    ],
    standalone: true
})
export class TestDialogComponent {

    constructor(private modalCtrl: ModalController) {

    }

    async close() {
        await this.modalCtrl.dismiss();
    }

}

// use a mock-class so we can directly spy on it
class ModalControllerMock {
    dismiss() {
        return Promise.resolve();
    }
}

describe('TestDialogComponent', () => {
    let component: TestDialogComponent;
    let fixture: ComponentFixture<TestDialogComponent>;
    const modalControllerMock = new ModalControllerMock();

    beforeEach(async () => {
        await TestBed.configureTestingModule({
            imports: [
                BrowserModule,
                IonicModule.forRoot(),
                TestDialogComponent
            ]
        }).compileComponents();
        // use this provider instead of the provider in configureTestingModule
        TestBed.overrideComponent(TestDialogComponent, {
            set: {
                providers: [{  provide: ModalController, useValue: modalControllerMock}],
            },
        });
        fixture = TestBed.createComponent(TestDialogComponent);
        component = fixture.componentInstance;
    });

    it('close closes the dialog', async () => {
        const dismissSpy = spyOn(modalControllerMock, 'dismiss');
        await component.close();
        expect(dismissSpy).toHaveBeenCalled();
    });

});

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