react-native-reanimated-carousel/lib/module/hooks/index.test.js

Simple carousel component.fully implemented using Reanimated 2.Infinitely scrolling, very smooth.

import { computeNewIndexWhenDataChanges } from "./computeNewIndexWhenDataChanges";
describe("should work as expected", () => {
  const size = 375;
  const positive = -1;
  const negative = 1;

  const params = params => {
    const {
      currentIndex,
      direction: _direction,
      previousLength,
      currentLength
    } = params;
    const direction = _direction === "negative" ? negative : positive;
    return {
      direction,
      handlerOffset: size * currentIndex * direction,
      size,
      previousLength,
      currentLength
    };
  };

  it("The direction is negative, And changing length of data set from 4 to 3, the new index will to be 2.", async () => {
    const currentIndex = 1;
    const handlerOffset = computeNewIndexWhenDataChanges(params({
      currentIndex,
      direction: "negative",
      previousLength: 4,
      currentLength: 3
    }));
    expect(handlerOffset / size).toBe(2 * positive);
  });
  it("The direction is negative, Changing length of data set from 4 to 3, the index remains original.", async () => {
    const handlerOffset = computeNewIndexWhenDataChanges(params({
      currentIndex: 2,
      direction: "negative",
      previousLength: 4,
      currentLength: 3
    }));
    expect(handlerOffset / size).toBe(1 * negative);
  });
  it("The direction is positive, Changing length of data set from 4 to 5, the index remains original.", async () => {
    const handlerOffset = computeNewIndexWhenDataChanges(params({
      currentIndex: 3,
      direction: "positive",
      previousLength: 4,
      currentLength: 5
    }));
    expect(handlerOffset / size).toBe(3 * positive);
  });
  it("The direction is negative, Changing length of data set from 4 to 5, the index remains original.", async () => {
    const handlerOffset = computeNewIndexWhenDataChanges(params({
      currentIndex: 3,
      direction: "negative",
      previousLength: 4,
      currentLength: 5
    }));
    expect(handlerOffset / size).toBe(4 * negative);
  });
  it("Changing length of data set from 0 to 3, the index remains original.", async () => {
    const handlerOffset = computeNewIndexWhenDataChanges(params({
      currentIndex: 0,
      direction: "positive",
      previousLength: 0,
      currentLength: 3
    }));
    expect(handlerOffset / size).toBe(0 * positive);
  });
});
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