TestBed configuration in Angular - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the necessary Angular testing module.

Angular

TestBed.configureTestingModule({ imports: [[1]] });

Drag options to blanks, or click blank then click option'

AHttpClientTestingModule

BBrowserModule

CFormsModule

DRouterModule

Attempts:

3 left

💡 Hint

Common Mistakes

Using BrowserModule instead of HttpClientTestingModule

Forgetting to import any module

The HttpClientTestingModule is used to mock HTTP requests in Angular tests.

2fill in blank

medium

Complete the code to declare the component under test.

Angular

TestBed.configureTestingModule({ declarations: [[1]] });

Drag options to blanks, or click blank then click option'

AFormsModule

BHttpClientTestingModule

CAppComponent

DRouterTestingModule

Attempts:

3 left

💡 Hint

Common Mistakes

Putting modules inside declarations

Not declaring the component at all

The component to test must be declared in the declarations array.

3fill in blank

hard

Fix the error in the TestBed setup to create a component fixture.

Angular

const fixture = TestBed.[1](AppComponent);

Drag options to blanks, or click blank then click option'

AcompileComponents

Binject

CconfigureTestingModule

DcreateComponent

Attempts:

3 left

💡 Hint

Common Mistakes

Using compileComponents instead of createComponent

Trying to inject component directly

createComponent creates a test fixture for the component.

4fill in blank

hard

Fill both blanks to properly configure TestBed with declarations and imports.

Angular

TestBed.configureTestingModule({ declarations: [[1]], imports: [[2]] });

Drag options to blanks, or click blank then click option'

AAppComponent

BHttpClientTestingModule

CFormsModule

DRouterTestingModule

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping declarations and imports

Forgetting to import testing modules

The component goes in declarations, and the HTTP testing module goes in imports.

5fill in blank

hard

Fill all three blanks to create a TestBed configuration with declarations, imports, and providers.

Angular

TestBed.configureTestingModule({ declarations: [[1]], imports: [[2]], providers: [[3]] });

Drag options to blanks, or click blank then click option'

AAppComponent

BHttpClientTestingModule

CMyService

DFormsModule

Attempts:

3 left

💡 Hint

Common Mistakes

Putting services in imports or declarations

Forgetting to provide services

Declare the component, import the HTTP testing module, and provide the service for dependency injection.

Practice

1. What is the main purpose of Angular's TestBed in unit testing?

easy

A. To create a small Angular environment for testing components and services

B. To compile the entire Angular application for production

C. To replace Angular modules with plain JavaScript modules

D. To generate HTML templates automatically

Solution

1. Step 1: Understand TestBed's role

   TestBed sets up a lightweight Angular environment to test parts of your app without running the full app.

2. Step 2: Compare options

   Only To create a small Angular environment for testing components and services describes this testing environment purpose. Others describe unrelated tasks.

3. Final Answer:

   To create a small Angular environment for testing components and services -> Option A

4. Quick Check:

   TestBed purpose = create test environment [OK]

Hint: TestBed sets up Angular test environment, not full app build [OK]

Common Mistakes:

• Confusing TestBed with production build tools
• Thinking TestBed generates templates automatically
• Assuming TestBed replaces Angular modules

2. Which of the following is the correct way to declare a component in TestBed configuration?

easy

A. TestBed.configureTestingModule({ imports: [MyComponent] })

B. TestBed.configureTestingModule({ bootstrap: [MyComponent] })

C. TestBed.configureTestingModule({ providers: [MyComponent] })

D. TestBed.configureTestingModule({ declarations: [MyComponent] })

Solution

1. Step 1: Identify where components go in TestBed

   Components must be listed under declarations in the configuration.

2. Step 2: Check each option

   Only TestBed.configureTestingModule({ declarations: [MyComponent] }) uses declarations with the component. Others misuse imports, providers, or bootstrap.

3. Final Answer:

   TestBed.configureTestingModule({ declarations: [MyComponent] }) -> Option D

4. Quick Check:

   Components go in declarations [OK]

Hint: Components go in declarations, modules in imports, services in providers [OK]

Common Mistakes:

• Putting components inside imports or providers
• Using bootstrap in TestBed config (only for app modules)
• Forgetting to declare components causes errors

3. Given this TestBed setup, what will fixture.componentInstance.title output?

TestBed.configureTestingModule({
  declarations: [MyComponent]
}).compileComponents();

const fixture = TestBed.createComponent(MyComponent);
fixture.detectChanges();

// MyComponent code:
// title = 'Hello Test';

medium

A. null

B. 'Hello Test'

C. undefined

D. Error: Component not declared

Solution

1. Step 1: Confirm component declaration and compilation

   MyComponent is declared and compiled, so it can be created and used.

2. Step 2: Understand fixture and detectChanges

   Creating fixture and calling detectChanges initializes component and bindings, so title is set.

3. Final Answer:

   'Hello Test' -> Option B

4. Quick Check:

   Declared + compiled + detectChanges = property accessible [OK]

Hint: Declare and compile components before accessing properties [OK]

Common Mistakes:

• Forgetting to call compileComponents causes errors
• Not calling detectChanges leaves properties uninitialized
• Assuming properties are undefined without initialization

4. What is the error in this TestBed setup?

TestBed.configureTestingModule({
  declarations: [MyComponent]
});

const fixture = TestBed.createComponent(MyComponent);
fixture.detectChanges();

medium

A. detectChanges() should be called before createComponent()

B. MyComponent should be in imports, not declarations

C. Missing call to compileComponents() before createComponent()

D. No error, this setup is correct

Solution

1. Step 1: Check TestBed configuration steps

   When testing components with templates, compileComponents() must be called to compile templates asynchronously.

2. Step 2: Identify missing step

   The code misses compileComponents() before creating the component, which can cause errors.

3. Final Answer:

   Missing call to compileComponents() before createComponent() -> Option C

4. Quick Check:

   compileComponents() required before createComponent() [OK]

Hint: Always call compileComponents() before createComponent() for templates [OK]

Common Mistakes:

• Skipping compileComponents() causes template errors
• Putting components in imports instead of declarations
• Calling detectChanges() too early

5. You want to test a component that uses a service injected via constructor. Which TestBed configuration is correct to provide the service mock?

hard

A. TestBed.configureTestingModule({ declarations: [MyComponent], providers: [{ provide: MyService, useValue: mockService }] })

B. TestBed.configureTestingModule({ declarations: [MyComponent], imports: [MyService] })

C. TestBed.configureTestingModule({ declarations: [MyComponent], declarations: [MyService] })

D. TestBed.configureTestingModule({ providers: [MyComponent, MyService] })

Solution

1. Step 1: Understand service injection in TestBed

   Services are provided via providers array. To mock a service, use provide with useValue.

2. Step 2: Analyze options

   TestBed.configureTestingModule({ declarations: [MyComponent], providers: [{ provide: MyService, useValue: mockService }] }) correctly provides a mock service. TestBed.configureTestingModule({ declarations: [MyComponent], imports: [MyService] }) wrongly puts service in imports. TestBed.configureTestingModule({ declarations: [MyComponent], declarations: [MyService] }) wrongly declares service as component. TestBed.configureTestingModule({ providers: [MyComponent, MyService] }) wrongly provides component as service.

3. Final Answer:

   TestBed.configureTestingModule({ declarations: [MyComponent], providers: [{ provide: MyService, useValue: mockService }] }) -> Option A

4. Quick Check:

   Mock services go in providers with provide/useValue [OK]

Hint: Use providers with provide and useValue for service mocks [OK]

Common Mistakes:

• Putting services in imports or declarations
• Providing components instead of services
• Not mocking services causing real calls