Pipes have only one method, transform, that manipulates the input value into a transformed output value.
transform implementation rarely interacts with the DOM and most pipes have no dependencies other than the Angular @Pipe metada and interface.
An example of testing could be.
title-case.pipe.ts
import {Pipe, PipeTransform} from '@angular/core';
@Pipe({name: 'titlecase', pure: true})
/** Transform to Title Case: uppercase the first letter of the words in a string. */
export class TitleCasePipe implements PipeTransform {
transform(input: string): string {
return input.length === 0
? ''
: input.replace(/\w\S*/g, (txt) => txt[0].toUpperCase() + txt.slice(1).toLowerCase());
}
}
title-case.pipe.specs.ts
describe('TitleCasePipe', () => {
// This pipe is a pure, stateless function so no need for BeforeEach
const pipe = new TitleCasePipe();
it('transforms "abc" to "Abc"', () => {
expect(pipe.transform('abc')).toBe('Abc');
});
it('transforms "abc def" to "Abc Def"', () => {
expect(pipe.transform('abc def')).toBe('Abc Def');
});
});
