Add mock PPEC gateway

modules/ppcp-compat/services.php

@@ -9,4 +9,18 @@ declare(strict_types=1);
 
 namespace WooCommerce\PayPalCommerce\Compat;
 
-return array();
+return array(
+
+	'compat.ppec.mock-gateway' => static function( $container ) {
+		$settings = $container->get( 'wcgateway.settings' );
+		$title    = $settings->has( 'title' ) ? $settings->get( 'title' ) : __( 'PayPal', 'woocommerce-paypal-payments' );
+		$title    = sprintf(
+			/* Translators: placeholder is the gateway name. */
+			__( '%s (Legacy)', 'woocommerce-paypal-payments' ),
+			$title
+		);
+
+		return new PPEC\MockGateway( $title );
+	},
+
+);

modules/ppcp-compat/src/PPEC/class-mockgateway.php

@@ -0,0 +1,49 @@
+<?php
+/**
+ * Mock PayPal Express Checkout class.
+ *
+ * @package WooCommerce\PayPalCommerce\Compat\PPEC
+ */
+
+namespace WooCommerce\PayPalCommerce\Compat\PPEC;
+
+/**
+ * Mocks the PayPal Express Checkout gateway.
+ */
+class MockGateway extends \WC_Payment_Gateway {
+
+	/**
+	 * Constructor.
+	 *
+	 * @param string $title Gateway title.
+	 */
+	public function __construct( $title ) {
+		$this->id           = PPECHelper::PPEC_GATEWAY_ID;
+		$this->title        = $title;
+		$this->method_title = $this->title;
+		$this->description  = '';
+		$this->supports     = array(
+			'subscriptions',
+			'subscription_cancellation',
+			'subscription_suspension',
+			'subscription_reactivation',
+			'subscription_amount_changes',
+			'subscription_date_changes',
+			'subscription_payment_method_change',
+			'subscription_payment_method_change_customer',
+			'subscription_payment_method_change_admin',
+			'multiple_subscriptions',
+		);
+	}
+
+	/**
+	 * Check if the gateway is available for use.
+	 *
+	 * @return bool
+	 */
+	public function is_available() {
+		// Hide mock gateway, except on admin.
+		return is_admin();
+	}
+
+}