Why testing Angular apps matters - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a basic Angular test setup for a component.

Angular

beforeEach(() => {
  TestBed.configureTestingModule({
    declarations: [[1]]
  }).compileComponents();
});

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

AAppComponent

BHttpClientModule

CFormsModule

DRouterModule

Attempts:

3 left

💡 Hint

Common Mistakes

Putting modules like HttpClientModule in declarations instead of imports.

Forgetting to declare the component under test.

The declarations array should include the component you want to test, such as AppComponent.

2fill in blank

medium

Complete the code to create a test that checks if the component is created successfully.

Angular

it('should create the component', () => {
  const fixture = TestBed.createComponent(AppComponent);
  const component = fixture.componentInstance;
  expect(component).[1];
});

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

AtoBeNull()

BtoBeUndefined()

CtoBeTruthy()

DtoBeFalse()

Attempts:

3 left

💡 Hint

Common Mistakes

Using toBeNull() which expects the value to be null.

Using toBeFalse() which expects the value to be false.

Using toBeTruthy() checks that the component instance exists and is truthy, meaning it was created.

3fill in blank

hard

Fix the error in the test by completing the code to detect changes after setting a component property.

Angular

it('should update title in template', () => {
  const fixture = TestBed.createComponent(AppComponent);
  const component = fixture.componentInstance;
  component.title = 'Test Title';
  fixture.[1]();
  const compiled = fixture.nativeElement as HTMLElement;
  expect(compiled.querySelector('h1')?.textContent).toContain('Test Title');
});

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

AdetectChanges

BupdateView

Crefresh

DapplyChanges

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent methods like updateView or refresh.

Forgetting to call detectChanges causing the template not to update.

Calling fixture.detectChanges() tells Angular to update the template with the latest component data.

4fill in blank

hard

Fill both blanks to import necessary modules and declare the component in the test setup.

Angular

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

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

AHttpClientTestingModule

BAppComponent

CFormsModule

DRouterTestingModule

Attempts:

3 left

💡 Hint

Common Mistakes

Putting components in imports or modules in declarations.

Forgetting to import testing modules needed by the component.

HttpClientTestingModule is imported to mock HTTP requests, and AppComponent is declared to test it.

5fill in blank

hard

Fill all three blanks to create a test that spies on a service method and checks if it was called.

Angular

it('should call fetchData from service', () => {
  const fixture = TestBed.createComponent(DataComponent);
  const component = fixture.componentInstance;
  const service = TestBed.inject(DataService);
  spyOn(service, '[1]').and.returnValue(of([]));
  component.loadData();
  expect(service.[2]).toHaveBeenCalled();
  expect(component.data).toEqual([3]);
});

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

AfetchData

C[]

D{}

Attempts:

3 left

💡 Hint

Common Mistakes

Using different method names in spyOn and expect.

Expecting data to be an object instead of an array.

The test spies on the fetchData method, expects it to be called, and checks that the component's data is an empty array [] as returned by the spy.

Practice

1. Why is testing important in Angular applications?

easy

A. It automatically writes code for you

B. It helps find errors before users encounter them

C. It reduces the size of the app bundle

D. It makes the app run faster

Solution

1. Step 1: Understand the purpose of testing

   Testing is used to catch bugs and errors early in development before users see them.

2. Step 2: Compare options with testing goals

   Only It helps find errors before users encounter them matches the goal of testing by helping find errors early.

3. Final Answer:

   It helps find errors before users encounter them -> Option B

4. Quick Check:

   Testing finds errors early = D [OK]

Hint: Testing finds bugs early to avoid user problems [OK]

Common Mistakes:

• Thinking testing improves app speed
• Confusing testing with code optimization
• Believing testing writes code automatically

2. Which of the following is the correct way to import Angular testing utilities in a test file?

easy

A. import { HttpClient } from '@angular/common/http';

B. import { Component } from '@angular/core';

C. import { RouterModule } from '@angular/router';

D. import { TestBed } from '@angular/core/testing';

Solution

1. Step 1: Identify Angular testing imports

   Angular testing utilities like TestBed come from '@angular/core/testing'.

2. Step 2: Match import statements

   Only import { TestBed } from '@angular/core/testing'; imports TestBed from the correct testing module.

3. Final Answer:

   import { TestBed } from '@angular/core/testing'; -> Option D

4. Quick Check:

   TestBed import = A [OK]

Hint: TestBed is from '@angular/core/testing' for tests [OK]

Common Mistakes:

• Importing Component instead of TestBed
• Using RouterModule or HttpClient in test imports
• Confusing core and testing modules

3. Given this Angular test snippet, what will be the output when the test runs?

describe('Simple test', () => {
  it('should pass', () => {
    expect(true).toBe(true);
  });
});

medium

A. Test passes successfully

B. Test fails with error

C. Test is skipped

D. Syntax error occurs

Solution

1. Step 1: Analyze the test condition

   The test expects true to be true, which is always correct.

2. Step 2: Determine test result

   Since the expectation matches, the test will pass without errors.

3. Final Answer:

   Test passes successfully -> Option A

4. Quick Check:

   expect(true).toBe(true) passes = B [OK]

Hint: True equals true means test passes [OK]

Common Mistakes:

• Thinking the test fails due to syntax
• Assuming test is skipped without skip keyword
• Confusing test pass with runtime error

4. What is wrong with this Angular test code snippet?

describe('MyComponent', () => {
  it('should create', () => {
    const fixture = TestBed.createComponent(MyComponent);
    const component = fixture.componentInstance;
    expect(component).toBeDefined;
  });
});

medium

A. componentInstance is undefined

B. TestBed.createComponent is not a function

C. Missing parentheses after toBeDefined

D. describe block is missing

Solution

1. Step 1: Check the expect statement syntax

   The expect statement uses toBeDefined without parentheses, which is incorrect.

2. Step 2: Understand correct matcher usage

   Matchers like toBeDefined must be called as functions with parentheses: toBeDefined().

3. Final Answer:

   Missing parentheses after toBeDefined -> Option C

4. Quick Check:

   toBeDefined() needs () = C [OK]

Hint: Matchers need () after them to run [OK]

Common Mistakes:

• Forgetting parentheses on matchers
• Assuming createComponent is undefined
• Thinking componentInstance is missing

5. You want to ensure your Angular app's login component works correctly after changes. Which testing approach best helps catch errors early and maintain app quality?

hard

A. Write unit tests for the login component and run them automatically on each code change

B. Only test the login component manually before release

C. Skip testing and fix bugs reported by users

D. Write tests only after the app is fully deployed

Solution

1. Step 1: Identify best testing practice for quality

   Writing unit tests and running them automatically helps catch errors early and keeps quality high.

2. Step 2: Compare options for effectiveness

   Only Write unit tests for the login component and run them automatically on each code change describes proactive, automated testing which is best practice.

3. Final Answer:

   Write unit tests for the login component and run them automatically on each code change -> Option A

4. Quick Check:

   Automated unit tests catch errors early = A [OK]

Hint: Automate tests early to catch bugs fast [OK]

Common Mistakes:

• Relying only on manual testing
• Ignoring tests until after deployment
• Waiting for user bug reports