Unit Testing Angular Components with Karma and Jasmine: Exploring Test Scope

Question

Unit Testing Angular Components with Karma and Jasmine: Exploring Test Scope

After reading various guides on unit testing, I have gained an understanding that in unit testing, the focus is on testing the logic within a component, with children components tested separately. Despite this knowledge, I still find myself uncertain about what exactly should be tested.

For example, consider the following scenario: There is an overview component which contains 2 children components, <app-refresh-button> and <canvas baseChart ...>, utilizing the ng2-charts wrapper library (chartjs).

<h1>Overview</h1>

<app-refresh-button 
  [isLoading]="isLoading"
  (onIntervalChange)="onSelectNewInterval($event)" 
  (onRefresh)="onRefreshManualClick($event)">
</app-refresh-button>

<canvas baseChart 
    [datasets]="lineChartData"
    ... ...
    (chartclick)="onChartClicked($event)"
</canvas>

When the refresh button is clicked, data points are added to the lineChartData array and displayed on the graph.

My confusion arises here:

Considering <app-refresh-button> as a child component, do I exclude it from unit testing?
If they are not tested together, how can I ensure that the logic in the refresh button and the graph plotting work cohesively?
Should functions like "pushingNewDataPoints()", responsible for updating the lineChartData array in the overview component, be included in the tests?

angular unit-testing karma-jasmine

Answer 1

Answer №1

Since this is a child component, it's not necessary to include it in unit tests, correct?

Correct, you shouldn't test it in unit tests.

If the logic in the refresh button and graph plotting are interconnected, how can I ensure they work together if they are not tested simultaneously?

I see two possible solutions:

Shallow/Integration tests - in these tests, real components and dependencies are provided so interactions can be checked with actual implementations. However, heavy services/modules like HttpClientModule or RouterModule should be excluded or substituted with testing equivalents.
Another option is to create simple mocks of child components for testing purposes. These mocks enable testing of specific cases (events, data setting, etc.) by triggering events using methods like triggerEventHandler from DebugElement. It's also possible to completely omit providing child components (exercise caution) and trigger events using dispatchEvent method from HTMLElement as described here: https://angular.io/guide/testing#no_errors_schema.

Regarding functions like "pushingNewDataPoints()" which add new data to the lineChartData array within this overview component, should they be tested?

Considering that lineChartData is public, you can simulate an event on app-refresh-button that manipulates lineChartData and then verify if it contains the expected values.

Answer 2

Since this is a child component, it's not necessary to include it in unit tests, correct?

Correct, you shouldn't test it in unit tests.

If the logic in the refresh button and graph plotting are interconnected, how can I ensure they work together if they are not tested simultaneously?

I see two possible solutions:

Shallow/Integration tests - in these tests, real components and dependencies are provided so interactions can be checked with actual implementations. However, heavy services/modules like HttpClientModule or RouterModule should be excluded or substituted with testing equivalents.
Another option is to create simple mocks of child components for testing purposes. These mocks enable testing of specific cases (events, data setting, etc.) by triggering events using methods like triggerEventHandler from DebugElement. It's also possible to completely omit providing child components (exercise caution) and trigger events using dispatchEvent method from HTMLElement as described here: https://angular.io/guide/testing#no_errors_schema.

Regarding functions like "pushingNewDataPoints()" which add new data to the lineChartData array within this overview component, should they be tested?

Considering that lineChartData is public, you can simulate an event on app-refresh-button that manipulates lineChartData and then verify if it contains the expected values.

Answer 3

Answer №2

Answering this question poses a challenge, as it heavily relies on personal opinions.

In my perspective, I recommend focusing on testing all property bindings and event bindings of the child components without delving into how the actual component handles these inputs and outputs.

An effective way to set this up is by utilizing the NO_ERRORS_SCHEMA within your TestBed configuration.

With this setup, you can use triggerEventHandler for event bindings.

const debugElem = fixture.debugElement.get(By.css('app-refresh-button'));
debugElem.triggerEventHandler('onIntervalChange', THE_EVENT_DATA_YOU_WANT_TO_USE_INSIDE_THE_TEST)

tick();

expect()...

For property bindings, you can also access these properties from the debugElement:

const debugElem = fixture.debugElement.get(By.css('app-refresh-button'));
expect(debugElem.properties['isLoading']).toEqual(...)

By employing these methods, you can verify that an output from the refresh button impacts the input in your canvas, among other scenarios, without explicitly testing the component's behavior with those inputs and outputs.

I hope this explanation proves beneficial.

Answer 4

Answering this question poses a challenge, as it heavily relies on personal opinions.

In my perspective, I recommend focusing on testing all property bindings and event bindings of the child components without delving into how the actual component handles these inputs and outputs.

An effective way to set this up is by utilizing the NO_ERRORS_SCHEMA within your TestBed configuration.

With this setup, you can use triggerEventHandler for event bindings.

const debugElem = fixture.debugElement.get(By.css('app-refresh-button'));
debugElem.triggerEventHandler('onIntervalChange', THE_EVENT_DATA_YOU_WANT_TO_USE_INSIDE_THE_TEST)

tick();

expect()...

For property bindings, you can also access these properties from the debugElement:

const debugElem = fixture.debugElement.get(By.css('app-refresh-button'));
expect(debugElem.properties['isLoading']).toEqual(...)

By employing these methods, you can verify that an output from the refresh button impacts the input in your canvas, among other scenarios, without explicitly testing the component's behavior with those inputs and outputs.

I hope this explanation proves beneficial.

Unit Testing Angular Components with Karma and Jasmine: Exploring Test Scope

Answer №1

Answer №2

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