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How to test a structural directive with a context in Angular application

If you did not read "How to test a structural directive", please do it first.

The difference for structural directives with a context in terms of testing is that our custom template has variables.

const fixture = MockRender(
`<div *target="values; let value; let index = myIndex">
{{index}}: {{ value }}
</div>`,
{
values: ['hello', 'world'],
}
);

This directive simulates behavior of *ngFor. We can do different assertions checking rendered html, and to verify how the directive behaves when we are changing values:

expect(fixture.nativeElement.innerHTML).toContain('0: hello');
expect(fixture.nativeElement.innerHTML).toContain('1: world');
fixture.componentInstance.values = ['ng-mocks'];
fixture.detectChanges();
expect(fixture.nativeElement.innerHTML).toContain('0: ng-mocks');
expect(fixture.nativeElement.innerHTML).not.toContain('0: hello');
expect(fixture.nativeElement.innerHTML).not.toContain('1: world');

Live example

https://github.com/ike18t/ng-mocks/blob/master/examples/TestStructuralDirectiveWithContext/test.spec.ts
import {
Directive,
Input,
TemplateRef,
ViewContainerRef,
} from '@angular/core';
import { MockBuilder, MockRender } from 'ng-mocks';

export interface ITargetContext {
$implicit: string;
myIndex: number;
}

// This directive is almost the same as `ngFor`,
// it renders every item as a new row.
@Directive({
selector: '[target]',
})
class TargetDirective {
public constructor(
protected templateRef: TemplateRef<ITargetContext>,
protected viewContainerRef: ViewContainerRef,
) {}

@Input() public set target(items: string[]) {
this.viewContainerRef.clear();

for (let index = 0; index <= items.length; index += 1) {
const value = items[index];
this.viewContainerRef.createEmbeddedView(this.templateRef, {
$implicit: value,
myIndex: index,
});
}
}
}

describe('TestStructuralDirectiveWithContext', () => {
// Because we want to test the directive, we pass it as the first
// parameter of MockBuilder. We can omit the second parameter,
// because there are no dependencies.
// Do not forget to return the promise of MockBuilder.
beforeEach(() => MockBuilder(TargetDirective));

it('renders passed values', () => {
const fixture = MockRender(
`
<div *target="values; let value; let index = myIndex">
{{index}}: {{ value }}
</div>
`,
{
values: ['hello', 'world'],
},
);

// Let's assert that the 'values' have been rendered as expected
expect(fixture.nativeElement.innerHTML).toContain('0: hello');
expect(fixture.nativeElement.innerHTML).toContain('1: world');

// Let's change the 'values' and assert that the new render
// has done everything as expected.
fixture.componentInstance.values = ['ngMocks'];
fixture.detectChanges();
expect(fixture.nativeElement.innerHTML).toContain('0: ngMocks');
expect(fixture.nativeElement.innerHTML).not.toContain('0: hello');
expect(fixture.nativeElement.innerHTML).not.toContain('1: world');
});
});