Add unit test and a sample Woo plugin file

sample-woo-plugin.php

@@ -0,0 +1,6 @@
+<?php // phpcs:ignoreFile
+/**
+ * Plugin Name: Sample WooCommerce PLugin
+ * Woo: 1:sample-woo-plugin
+ */
+

tests/legacy/bootstrap.php

@@ -44,6 +44,15 @@ class WC_Unit_Tests_Bootstrap {
 		$this->plugin_dir   = dirname( dirname( $this->tests_dir ) );
 		$this->wp_tests_dir = getenv( 'WP_TESTS_DIR' ) ? getenv( 'WP_TESTS_DIR' ) : sys_get_temp_dir() . '/wordpress-tests-lib';
 
+		if ( ! defined( 'WP_PLUGIN_DIR' ) ) {
+			define( 'WP_PLUGIN_DIR', $this->plugin_dir );
+		}
+
+		if ( file_exists( WP_PLUGIN_DIR . '/sample-woo-plugin.php' ) ) {
+			unlink( WP_PLUGIN_DIR . '/sample-woo-plugin.php' );
+		}
+		copy( __DIR__ . '/data/sample-woo-plugin.php', WP_PLUGIN_DIR . '/sample-woo-plugin.php' );
+
 		// load test function so tests_add_filter() is available.
 		require_once $this->wp_tests_dir . '/includes/functions.php';
 

tests/legacy/data/sample-woo-plugin.php

@@ -0,0 +1,6 @@
+<?php // phpcs:ignoreFile
+/**
+ * Plugin Name: Sample WooCommerce PLugin
+ * Woo: 1:sample-woo-plugin
+ */
+

tests/php/includes/admin/helper/class-tests-wc-helper.php

@@ -0,0 +1,33 @@
+<?php
+/**
+ * Class WC_Tests_WC_Helper file.
+ *
+ * @package WooCommerce|Tests|WC_Helper.
+ */
+
+/**
+ * Class WC_Tests_WC_Helper.
+ */
+class WC_Tests_WC_Helper extends WC_Unit_Test_Case {
+
+	/**
+	 * Test that woo plugins are loaded correctly even if incorrect cache is intially set.
+	 */
+	public function test_get_local_woo_plugins_without_woo_header_cache() {
+		$woocommerce_key = 'sample-woo-plugin.php';
+
+		remove_filter( 'extra_plugin_headers', 'wc_enable_wc_plugin_headers' );
+		wp_clean_plugins_cache( false );
+		get_plugins();
+
+		add_filter( 'extra_plugin_headers', 'wc_enable_wc_plugin_headers' );
+
+		$woo_plugins = WC_Helper::get_local_woo_plugins();
+
+		// Restore previous state.
+		wp_clean_plugins_cache( false );
+
+		$this->assertArrayHasKey( $woocommerce_key, $woo_plugins );
+	}
+
+}