Because Travis isn't initializing the plugin tests correctly, copy in…

… the boilerplate from the 'wp scaffold plugin' command, without removing existing bootstrap.php functionality.

tests/bootstrap.php

@@ -1,12 +1,37 @@
 <?php
+/**
+ * PHPUnit bootstrap file
+ */
 
 $wp_tests_dir = getenv('WP_TESTS_DIR');
+if ( ! $wp_tests_dir ) {
+	$_tests_dir = rtrim( sys_get_temp_dir(), '/\\' ) . '/wordpress-tests-lib';
+}
+
+if ( ! file_exists( $wp_tests_dir . '/includes/functions.php' ) ) {
+	echo "Could not find $wp_tests_dir/includes/functions.php, have you run bin/install-wp-tests.sh ?" . PHP_EOL;
+	exit( 1 );
+}
+
+// Give access to tests_add_filter() function.
 require_once $wp_tests_dir . '/includes/functions.php';
 
+/**
+ * Make sure WordPress knows the plugin should be active
+ */
 function _manually_load_environment() {
 	$plugins_to_active = array("WP-DS-NPR-API/ds-npr-api.php");
-	update_option('active_plugins', $plugins_to_active);
+	update_option( 'active_plugins', $plugins_to_active );
+}
+tests_add_filter( 'muplugins_loaded', '_manually_load_environment' );
+
+/**
+ * Manually load the plugin being tested.
+ */
+function _manually_load_plugin() {
+	require dirname( dirname( __FILE__ ) ) . '/sample-plugin.php';
 }
-tests_add_filter('muplugins_loaded', '_manually_load_environment');
+tests_add_filter( 'muplugins_loaded', '_manually_load_plugin' );
 
+// Start up the WP testing environment.
 require $wp_tests_dir . '/includes/bootstrap.php';