forum/app/assets/javascripts/discourse/tests/integration/helpers/slice-test.js

import { run } from "@ember/runloop";
import { render } from "@ember/test-helpers";
import { hbs } from "ember-cli-htmlbars";
import { setupRenderingTest } from "ember-qunit";
import { module, test } from "qunit";

module("Integration | Helper | {{slice}}", function (hooks) {
  setupRenderingTest(hooks);

  test("it slices an array with positional params", async function (assert) {
    this.set("array", [2, 4, 6]);

    await render(hbs`
      {{slice 1 3 this.array}}
    `);

    assert.dom().hasText("4,6", "sliced values");
  });

  test("it slices when only 2 params are passed", async function (assert) {
    this.set("array", [2, 4, 6]);

    await render(hbs`
      {{slice 1 this.array}}
    `);

    assert.dom().hasText("4,6", "sliced values");
  });

  test("it recomputes the slice if an item in the array changes", async function (assert) {
    let array = [2, 4, 6];
    this.set("array", array);

    await render(hbs`
      {{slice 1 3 this.array}}
    `);

    assert.dom().hasText("4,6", "sliced values");

    run(() => array.replace(2, 1, [5]));

    assert.dom().hasText("4,5", "sliced values");
  });

  test("it allows null array", async function (assert) {
    this.set("array", null);

    await render(hbs`
      this is all that will render
      {{#each (slice 1 2 this.array) as |value|}}
        {{value}}
      {{/each}}
    `);

    assert.dom().hasText("this is all that will render", "no error is thrown");
  });

  test("it allows undefined array", async function (assert) {
    this.set("array", undefined);

    await render(hbs`
      this is all that will render
      {{#each (slice 1 2 this.array) as |value|}}
        {{value}}
      {{/each}}
    `);

    assert.dom().hasText("this is all that will render", "no error is thrown");
  });
});