How to register a global directive in Vue for entire app

How can i register a Vue directive so it's available in all of my components of my Vue application? I'm using Vue 2

The docs say you can register global but where in my project do I add this Vue.directive(....)

src/directives/TestMe.js

import Vue from 'vue'

export default Vue.directive('test-me', {
  inserted(el) {
    el.style.backgroundColor = 'red'
  },
})

src/components/SignInForm.vue

<template>
    <div>
        <code v-test-me>
            Hello World
        </code>
    </div>

</template>

</script>

I know the current way of doing this by doing the following. However it's not practical if I plan on using my directive in multiple components and pages of my application.

<template>
    <div>
        <code v-test-me>
            Hello World
        </code>
    </div>
</template>

<script>
import TestMe from '../../directives/TestMe'
export default {
    directives: {
        TestMe
    }
}
</script>

Updated Updated post based on answers below.

I've created a different files for each directive and then have an index.js file where i import all my directives. How can i initiate that index.js file in the directives folder at the start of my application?

// src/directives/TestMe.js
export default testMe = {
  inserted(el) {
    el.style.backgroundColor = 'red'
  },
}

// src/directives/index.js
import testMe from './TestMe'

export default {
  install(Vue) {
    Vue.directive('test-me', testMe)
    // Vue.directive('other-directive', myOtherDirective)
  },
}

// src/main.js
import Vue from 'vue'
import App from './App.vue'
import ???? from './directives'

const app = createApp(App)
app.use(????)

You have globalDirectives...where does that name come from?

EDIT: I didn't read that OP is using Vue 2.

To call .use(), you need to export object with function install(Vue)

If you want the directive as a separate file.

// src/directives/TestMe.js

const testMe = {
  inserted(el) {
    el.style.backgroundColor = 'red'
  },
}
export default testMe

Here is where you register all the directives. You can import files or just define your directives here.

// src/directives/index.js

import testMe from './TestMe'

// const myOtherDirective = {
//   ...
// }

export default {
  install (Vue) {
    Vue.directive('test-me', testMe)
    // Vue.directive('other-directive', myOtherDirective)
  }
}

Here is how to register directives in Vue 2

You can register the global directives in main.js with Vue.use

// src/main.js

import Vue from 'vue'
import App from './App.vue'
import globalDirectives from './directives'
Vue.use(globalDirectives)

const app = new Vue({
  router,
  store,
  render: h => h(App),
})
app.$mount('#app')

Here is how to register directives in Vue 3

You can register the global directives in main.js after createApp

// src/main.js

import Vue from 'vue'
import App from './App.vue'
import globalDirectives from './directives'

const app = createApp(App)
app.use(globalDirectives)