Karma + Jamsine (Angular Testing): Where should I define mock classes and test variables

Lets take the following example:

const listDefinition: any = {
    module: "module",
    service: "service",
    listname: "listname"
};

@Component(...)
class MockTreeExpanderComponent extends TreeExpanderComponent {...}

class MockListConfigurationsService extends ListConfigurationsService {...}

describe('ColumnsListConfigurationsComponent Test cases', () => {
    let fixture: ComponentFixture<ColumnsListConfigurationsComponent>;
    let component: ColumnsListConfigurationsComponent;
    beforeEach(() => {
        TestBed.configureTestingModule({
            declarations: [
                ComponentToTest,
                MockTreeExpanderComponent
            ],
            providers: [
                 { provide: TreeListConfigurationService, useClass: MockTreeListConfigurationService }
            ]
        });
        fixture = TestBed.createComponent(ComponentToTest);
        component = fixture.componentInstance;
        component.listDefinition = listDefinition;
        fixture.detectChanges();
    });
});

As you can see, I have a Mock component (MockListViewerGridComponent) and service (ListConfigurationsService), a configuration variable (listDefinition) and the fixture and component that I want to test.

My question is about performance and test memory management:

1. The variables instantiated inside of describe method will be destroy as soon as the all tests inside of describe finishes?
2. Should I declare all variables and mock classes/services inside of describe?
3. Should I create a fixture in beforeEach or beforeAll? By doing that, I will have performance improvement?

Thank you!

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