Jest/Enzyme - Actions must be plain objects. Use custom middleware for async actions

I am trying to write a test for a React component using Jest and Enzyme but I keep on getting the same error Actions must be plain objects. Use custom middleware for async actions. no matter what I try. The component itself works as expected.

The component is:

import React, { Component } from 'react';
import { connect } from 'react-redux';
import { bindActionCreators } from 'redux';
import signUp from '../../actions/users/sign_up';
import PropTypes from 'prop-types';

class Signup extends Component {
  constructor (props) {
    super(props);

    this.handleChange = this.handleChange.bind(this);
    this.handleSubmit = this.handleSubmit.bind(this);
    this.showError = this.showError.bind(this);
  }

  handleChange(event) {
    const target = event.target;

    this.setState({ [ target.name ]: target.value });
  }

  handleSubmit(event) {
    event.preventDefault();
    this.props.signUp(this.state);
  }

  showError(type) {
    if (this.state && this.state.error && this.state.error.data.errors[ type ]) {
      return this.state.error.data.errors[ type ][ 0 ];
    }
  }

  componentDidUpdate (prevProps, prevState) {
    const props = this.props;

    if (prevProps === props) {
      return;
    }

    this.setState({
      ...props,
    });
  }

  render () {
    return (
        <div className='container-fluid'>
            <div className='row'>
                <div className='col col-md-6 offset-md-3 col-sm-12 col-12'>
                    <div className='card'>
                        <div className='card-header'>
                            <h4>Sign Up</h4>
                        </div>
                        <div className='card-body'>
                            <form onSubmit={ this.handleSubmit } >
                                <div className="form-row">
                                    <div className="form-group col-md-12">
                                        <label htmlFor="email">Email</label>
                                        <input
                        type="email"
                        name="email"
                        className={ `form-control ${ this.showError('email') ? 'is-invalid' : '' }` }
                        id="email"
                        placeholder="Email"
                        onChange={ this.handleChange }
                      />
                                        <div className="invalid-feedback">
                                            { this.showError('email') }
                                        </div>
                                    </div>
                                </div>
                                <div className="form-row">
                                    <div className="form-group col-md-12">
                                        <label htmlFor="username">Username</label>
                                        <input
                        type="text"
                        name="username"
                        className={ `form-control ${ this.showError('username') ? 'is-invalid' : '' }` }
                        id="username"
                        placeholder="Username"
                        onChange={ this.handleChange }
                      />
                                        <div className="invalid-feedback">
                                            { this.showError('username') }
                                        </div>
                                    </div>
                                </div>
                                <div className="form-row">
                                    <div className="form-group col-md-12">
                                        <label htmlFor="password">Password</label>
                                        <input
                          type="password"
                          name="password"
                          className={ `form-control ${ this.showError('password') ? 'is-invalid' : '' }` }
                          id="password"
                          placeholder="Password"
                          onChange={ this.handleChange }
                        />
                                        <div className="invalid-feedback">
                                            { this.showError('password') }
                                        </div>
                                    </div>
                                    <button type="submit" className="btn btn-primary">Sign Up</button>
                                </div>
                            </form>
                        </div>
                    </div>
                </div>
            </div>
        </div>
    )
  }
}

function mapStateToProps (state) {
  return {
    email: state.UsersReducer.email,
    username: state.UsersReducer.username,
    password: state.UsersReducer.password,
    error: state.UsersReducer.error,
  }
}

function mapDispatchToProps (dispatch) {
  return bindActionCreators({
    signUp: signUp,
  }, dispatch);
}

Signup.propTypes = {
  email: PropTypes.string,
  username: PropTypes.string,
  passwrod: PropTypes.string,
  signUp: PropTypes.func.isRequired
}

export default connect(mapStateToProps, mapDispatchToProps)(Signup);

The test I have so far is as follows:

import React from 'react';
import { shallow, mount } from 'enzyme';
import configureStore from 'redux-mock-store';

import Signup from '../../../components/users/signup';
import UsersReducer from '../../../reducers/reducer_users';

describe('<Signup />', () => {
  describe('render()', () => {
    test('submits the form data', () => {

      const mockStore = configureStore();

      const initialState = {
        UsersReducer: {
          email: '',
          username: '',
          password: '',
        },
      };

      const store = mockStore(initialState);

      const signUp = jest.fn();

      const wrapper = shallow(<Signup store={store} signUp={signUp} />);
      const component = wrapper.dive()

      component.find('#email').simulate(
        'change', {
          target: {
            name: 'email', value: 'foo@gmail.com'
          }
        }
      );

      component.find('#email').simulate(
        'change', {
          target: {
            name: 'username', value: 'foo'
          }
        }
      );

      component.find('#password').simulate(
        'change', {
          target: {
            name: 'password',
            value: '1234567',
          }
        }
      )
      console.log(wrapper.props())
      component.find('form').simulate(
        'submit', {
          preventDefault() {}
        }
      )

      expect(signUp.mock.calls[1][0]).toEqual(
        { email: 'foo@gmail.com', username: 'foo', password: '12345678' }
      )
    });
  });
});

The error Actions must be plain objects. Use custom middleware for async actions. keeps on being thrown handleSubmit:

  22 |   handleSubmit(event) {
  23 |     event.preventDefault();
> 24 |     this.props.signUp(this.state);
     |                ^
  25 |   }

Any help would be greatly appreciated as this is doing my head in!