@jetshop/core/experiments/selectExperimentVariant.test.js

import selectExperimentVariant from './selectExperimentVariant';

describe('selectExperimentVariant', () => {
  it('returns null if no config is supplied', () => {
    expect(selectExperimentVariant(null)).toBe(null);
  });

  it('returns the previous value if experiment matches the config', () => {
    const config = {
      experimentId: 'test',
      variantWeights: [0.5]
    };

    const selectedVariant = 'test.0';

    expect(selectExperimentVariant(config, selectedVariant)).toBe(
      selectedVariant
    );
  });

  it('returns a new value if experiment id is correct but variant is out of range', () => {
    const config = {
      experimentId: 'test',
      variantWeights: [1]
    };

    const selectedVariant = 'test.2';

    const newVariant = selectExperimentVariant(config, selectedVariant);
    expect(newVariant).not.toBe(selectedVariant);
    expect(newVariant).toBe('test.0');
  });

  it('returns a new value if experiment id is wrong', () => {
    const config = {
      experimentId: 'other',
      variantWeights: [1]
    };

    const selectedVariant = 'test.0';

    const newVariant = selectExperimentVariant(config, selectedVariant);
    expect(newVariant).not.toBe(selectedVariant);
    expect(newVariant).toBe('other.0');
  });

  it('selects a random variant if no previous one was provided', () => {
    const config = {
      experimentId: 'test',
      variantWeights: [0.25, 0.25, 0.25, 0.25]
    };

    expect(selectExperimentVariant(config, null)).not.toBe(null);
  });

  it('works if sum of variant weights is more than 1', () => {
    const config = {
      experimentId: 'test',
      variantWeights: [1, 1, 1, 1]
    };

    expect(selectExperimentVariant(config, null)).not.toBe(null);
  });
});