Setup code quality and tests

tests/Gateway_Functions_Test.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace WP_Ultimo\Tests;
+
+use WP_Ultimo\Gateways\Manual_Gateway;
+use WP_Ultimo\Managers\Gateway_Manager;
+
+class Gateway_Functions_Test extends \WP_UnitTestCase {
+
+	public function test_wu_get_gateway_returns_false_for_invalid_id() {
+	    $invalid_gateway_id = 'non_existent_gateway';
+
+	    $result = wu_get_gateway($invalid_gateway_id);
+
+	    $this->assertFalse($result);
+	}
+
+	public function test_wu_get_gateway_returns_instance_for_valid_id() {
+	    $valid_gateway_id = 'manual';
+
+	    $gateway = wu_get_gateway($valid_gateway_id);
+
+	    $this->assertInstanceOf(Manual_Gateway::class, $gateway);
+	}
+
+}