Test Plugin that programmatically registers a normal and italic Source Sans Pro with the Webfonts API

test-plugin-webfonts.php

<?php
/**
Plugin Name: Test Webfonts
Plugin URI: http://wordpress.org/plugins/test-plugin/
Description: Testing programmatically register webfonts from a plugin.
Author: me
Version: 1.0
*/


add_action(
	'after_setup_theme',
	function() {
		$webfonts = array(
			array(
				'font-family'  => 'Source Sans Pro',
				'font-style'   => 'normal',
				'font-stretch' => 'normal',
				'font-weight'  => '400',
				'src'          => 'http://localhost:8889/src/wp-content/plugins/test-plugin-webfonts/assets/fonts/SourceSansPro-Regular.ttf',
			),
			array(
				'font-family'  => 'Source Sans Pro',
				'font-style'   => 'normal',
				'font-stretch' => 'italic',
				'font-weight'  => '400',
				'src'          => 'http://localhost:8889/src/wp-content/plugins/test-plugin-webfonts/assets/fonts/SourceSansPro-Italic.ttf',
			)
		);
		wp_register_webfonts( $webfonts );
	},
	99
);