how test a reducer jest code example

Example: testing reducers with jest

// ./src/components/Todo.js
import React, { Component } from 'react'
import PropTypes from 'prop-types'
import moment from 'moment'
import {connect} from 'react-redux'
import {editTodo, toggleTodo, deleteTodo} from '../redux/actions'

export class Todo extends Component {
  constructor() {
    super();
    this.state = {
      formOpen: false,
      todo: {}
    }
    this.handleOpen=this.handleOpen.bind(this);
    this.handleClose=this.handleClose.bind(this);
    this.handleFieldChange=this.handleFieldChange.bind(this);
    this.handleEdit=this.handleEdit.bind(this);
    this.handleDelete=this.handleDelete.bind(this);
    this.handleToggle=this.handleToggle.bind(this);
  }

  // Open Todo edit form
  handleOpen() {
    this.setState({formOpen: true});
  }

  // Close Todo edit form and reset any changes
  handleClose() {
    this.setState({formOpen: false});
    this.setState({todo: {}});
  }
  // Handle changes to the input fields
  handleFieldChange(e) {
    // Property to change e.g title
    var field = e.target.name;
   // New value
    var value = e.target.value;
    var todo = this.state.todo;
    var todo = Object.assign({}, todo, {[field]: value});
    this.setState({todo: todo});
  }

  handleEdit() {
    // Send to-do id and new details to actions for updating
    this.props.editTodo(this.props.id, this.state.todo);
    this.handleClose();
  }

  handleDelete() {
   // Send to-do id to actions for deletion
    this.props.deleteTodo(this.props.id);
  }

  handleToggle() {
    // Mark a to-do as completed or incomplete
    this.props.toggleTodo(this.props.id, {done: !this.props.done})
  }

  render() {
    return (
      <div className="column">
        <div className="ui brown card">
          <img className="ui image" src={this.props.url} />
          {this.state.formOpen ?
            <div className="content">
              <div className='ui form'>
                <div className='field'>
                  <label>Title</label>
                  <input type='text'
                    name="title"
                    defaultValue={this.props.title}
                    onChange={this.handleFieldChange}
                  />
                </div>
                <div className='field'>
                  <label>Project</label>
                  <input type='text'
                    name="project"
                    defaultValue={this.props.project}
                    onChange={this.handleFieldChange}
                  />
                </div>
              </div>
            </div> :
            <div className="content">
              <div className="header">{this.props.title}</div>
              <div className="meta">{this.props.project}</div>
              <div className="meta">Created {moment(this.props.createdAt).fromNow()}</div>
            </div>
          }
          <div className="extra content">
            {this.state.formOpen ?
              <div className="ui two buttons">
                <button className='ui basic green button' onClick={this.handleEdit}>
                  <i className='checkmark icon'></i> Update
                </button>
                <button className='ui basic red button' onClick={this.handleClose}>
                  <i className='remove icon'></i> Cancel
                </button>
              </div> :
              <div>
                <div className="ui toggle checkbox" style={{marginBottom: '10px'}}>
                  <input type="checkbox" name="public" value="on" defaultChecked ={this.props.done} onChange={this.handleToggle}/>
                  <label>Complete</label>
                </div>
                <div className="ui two buttons">
                  <button className='ui basic green button' onClick={this.handleOpen}>Edit</button>
                  <button className="ui basic red button" onClick={this.handleDelete}>Delete</button>
                </div>
              </div>
            }
          </div>
        </div>
      </div>
    )
  }
}

Todo.propTypes = {
  id: PropTypes.string.isRequired,
  title: PropTypes.string.isRequired,
  project: PropTypes.string.isRequired,
  done: PropTypes.bool.isRequired,
  url: PropTypes.string.isRequired,
  createdAt: PropTypes.string.isRequired,
  editTodo: PropTypes.func.isRequired,
  toggleTodo: PropTypes.func.isRequired,
  deleteTodo: PropTypes.func.isRequired
};

export default connect(null, {editTodo, toggleTodo, deleteTodo})(Todo);