it('should be in array or throw error', () => { function showError() { unitSystem.prefix({sign: "none"}); } expect(showError).toThrowError(`Unsupported sign. Use: 'positive' or 'negative'`); expect(SI_PREFIXES._sym_.positive).toContain(unitSystem.prefix({ sign: 'positive', symbol: true })); expect(SI_PREFIXES._sym_.negative).toContain(unitSystem.prefix({ sign: 'negative', symbol: true })); expect(SI_PREFIXES.positive).toContain(unitSystem.prefix()); expect(SI_PREFIXES.negative).toContain(unitSystem.prefix({ sign: 'negative', symbol: false })); })