Demo

Install dependencies

npm init -y
npm install vue
npm install expect jsdom jsdom-global mocha mocha-webpack vue-loader vue-template-compiler vue-test-utils webpack --save-dev

package.json

"scripts": {
  "test": "mocha-webpack --webpack-config webpack.config.js --require test/setup.js test/*.spec.js",
  "watch": "mocha-webpack --webpack-config webpack.config.js --watch --require test/setup.js test/*.spec.js"
}

test/setup.js

require('jsdom-global')();

webpack.config.js

module.exports = {
    module: {
        rules: [
            {
                test: /\.vue$/,
                use: 'vue-loader'
            }
        ]
    }
};

src/components/Counter.vue

<template>
    <div>
        <span class="count" v-text="count"></span>
        <button @click="count++" class="increment">Increment</button>
        <button @click="count--" class="decrement" v-show="count > 0">Decrement</button>
    </div>
</template>

<script>
    export default {
        data() {
            return {
                count: 0
            };
        }
    }
</script>

test/counter.spec.js

import { mount } from 'vue-test-utils';
import Counter from '../src/components/Counter.vue';
import expect from 'expect';

describe ('Counter', () => {
    let wrapper;

    beforeEach(() => {
        wrapper = mount(Counter);
    });

    it('defaults to a count of 0', () => {
        expect(wrapper.vm.count).toBe(0);
    });

    it('increments the count when the increment button is clicked', () => {
        expect(wrapper.vm.count).toBe(0);
        wrapper.find('.increment').trigger('click');
        expect(wrapper.vm.count).toBe(1);
    });

    it('decrements the count when the decrement button is clicked', () => {
        wrapper.setData({ count: 5 });
        wrapper.find('.decrement').trigger('click');
        expect(wrapper.vm.count).toBe(4);
    });

    it('never goes below 0', () => {
        expect(wrapper.vm.count).toBe(0);
        expect(wrapper.find('.decrement').hasStyle('display', 'none')).toBe(true);
        wrapper.find('.increment').trigger('click');
        expect(wrapper.find('.decrement').hasStyle('display', 'none')).toBe(false);
    });

    it('presents the current count', () => {
        expect(wrapper.find('.count').html()).toContain(0);
        wrapper.find('.increment').trigger('click');
        expect(wrapper.find('.count').html()).toContain(1);
    });
});