Jest test case failing for React conditional

I am testing for the third conditional state error of the amount to equal a specific string, but when I run it I get an empty string.

Conditional:

if (!this.state.amount) {
    this.setState(() => ({ error: 'Please provide amount.' }));
}

Jest Test Case:

test('should render error for lack of amount', () => {
    const onSubmitSpy = jest.fn();
    const wrapper = shallow(<ExpenseForm expense={errors[1]} onSubmit={onSubmitSpy} />);
    expect(wrapper).toMatchSnapshot();
    wrapper.find('form').simulate('submit', {
        preventDefault: () => { },
    });
    expect(wrapper).toMatchSnapshot();
    console.log(wrapper.state('error'));
    expect(wrapper.state('error')).toBe('Please provide amount.');
}); 

Error array index:

id: '5',
description: 'Gas',
note: '',
amount: '',
createdAt: moment(0).add(4, 'days').valueOf()

Ideally, this condition should test for the amount state to equal '' and give the error message of 'Please provide amount.'