diff --git a/inc/admin-pages/class-dashboard-admin-page.php b/inc/admin-pages/class-dashboard-admin-page.php
index f81602a..d49fd01 100644
--- a/inc/admin-pages/class-dashboard-admin-page.php
+++ b/inc/admin-pages/class-dashboard-admin-page.php
@@ -488,15 +488,11 @@ class Dashboard_Admin_Page extends Base_Admin_Page {
 
 		$month_list = array();
 
-		$start = date_i18n('Y-m-d 00:00:00', strtotime('first day of january this year'));
+		$current_year = date_i18n('Y');
 
-		for ($i = 0; $i < 12; $i++) {
-
-			$start_date = wu_date($start);
-
-			$month_list[] = date_i18n('M y', $start_date->addMonths($i)->format('U'));
-
-		} // end for;
+		for ($i = 1; $i <= 12; $i++) {
+			$month_list[] = date_i18n('M y', mktime(0, 0,0,$i,1, $current_year));
+		}
 
 		$statistics = new Dashboard_Statistics(array(
 			'start_date' => $this->start_date,
diff --git a/inc/admin-pages/class-membership-edit-admin-page.php b/inc/admin-pages/class-membership-edit-admin-page.php
index 82d91c2..801ca87 100644
--- a/inc/admin-pages/class-membership-edit-admin-page.php
+++ b/inc/admin-pages/class-membership-edit-admin-page.php
@@ -128,7 +128,7 @@ class Membership_Edit_Admin_Page extends Edit_Admin_Page {
 			),
 		);
 
-		$date = wu_date($swap_order->scheduled_date);
+		$date = new \DateTime($swap_order->scheduled_date);
 
 		// translators: %s is the date, using the site format options
 		$message = sprintf(__('There is a change scheduled to take place on this membership in <strong>%s</strong>. You can preview the changes here. Scheduled changes are usually created by downgrades.', 'wp-ultimo'), $date->format(get_option('date_format')));
@@ -1078,7 +1078,7 @@ class Membership_Edit_Admin_Page extends Edit_Admin_Page {
 				),
 			);
 
-			$date = wu_date($swap_order->scheduled_date);
+			$date = new \DateTime($swap_order->scheduled_date);
 
 			// translators: %s is the date, using the site format options
 			$message = sprintf(__('This is a <strong>preview</strong>. This page displays the final stage of the membership after the changes scheduled for <strong>%s</strong>. Saving here will persist these changes, so be careful.', 'wp-ultimo'), $date->format(get_option('date_format')));
diff --git a/inc/deprecated/deprecated.php b/inc/deprecated/deprecated.php
index b044355..12997bb 100644
--- a/inc/deprecated/deprecated.php
+++ b/inc/deprecated/deprecated.php
@@ -1255,7 +1255,7 @@ class WU_Transactions {
 
 		_deprecated_function(__CLASS__, '2.0.0', 'wu_date()');
 
-		$date = wu_date();
+		$date = new \DateTime();
 
 		return $type === 'mysql' ? $date->format('Y-m-d H:i:s') : $date->format('U');
 
diff --git a/inc/domain-mapping/class-helper.php b/inc/domain-mapping/class-helper.php
index 830b7b6..c506c79 100644
--- a/inc/domain-mapping/class-helper.php
+++ b/inc/domain-mapping/class-helper.php
@@ -9,11 +9,10 @@
 
 namespace WP_Ultimo\Domain_Mapping;
 
-use Spatie\SslCertificate\SslCertificate;
 use Psr\Log\LogLevel;
 
 // Exit if accessed directly
-defined('ABSPATH') || exit;
+defined( 'ABSPATH' ) || exit;
 
 /**
  * Helper class for domain mapping functionality.
@@ -49,7 +48,7 @@ class Helper {
 
 		$site_url = site_url();
 
-		$is_development_mode = preg_match('#(localhost|staging.*\.|\.local|\.test)#', $site_url);
+		$is_development_mode = preg_match( '#(localhost|staging.*\.|\.local|\.test)#', $site_url );
 
 		/**
 		 * Allow plugin developers to add additional tests
@@ -61,21 +60,19 @@ class Helper {
 		 * @param string $site_url The site URL.
 		 * @return bool
 		 */
-		return apply_filters('wu_is_development_mode', $is_development_mode, $site_url);
-
+		return apply_filters( 'wu_is_development_mode', $is_development_mode, $site_url );
 	} // end is_development_mode;
- /**
-  * Gets the local IP address of the network.
-  *
-  * Sometimes, this will be the same address as the public one, but we need different methods.
-  *
-  * @since 2.0.0
-  * @return string|bool
-  */
- public static function get_local_network_ip() {
-
-		return isset($_SERVER['SERVER_ADDR']) ? $_SERVER['SERVER_ADDR'] : false;
+	/**
+	 * Gets the local IP address of the network.
+	 *
+	 * Sometimes, this will be the same address as the public one, but we need different methods.
+	 *
+	 * @since 2.0.0
+	 * @return string|bool
+	 */
+	public static function get_local_network_ip() {
 
+		return isset( $_SERVER['SERVER_ADDR'] ) ? $_SERVER['SERVER_ADDR'] : false;
 	} // end get_local_network_ip;
 
 	/**
@@ -90,43 +87,38 @@ class Helper {
 	 */
 	public static function get_network_public_ip() {
 
-		if (self::is_development_mode()) {
-
+		if ( self::is_development_mode() ) {
 			$local_ip = self::get_local_network_ip();
 
 			/**
 			 * See more about this filter below, on this same method.
 			 */
-			return apply_filters('wu_get_network_public_ip', $local_ip, true);
-
+			return apply_filters( 'wu_get_network_public_ip', $local_ip, true );
 		} // end if;
 
-		$_ip_address = get_site_transient('wu_public_network_ip');
-
-		if (!$_ip_address) {
+		$_ip_address = get_site_transient( 'wu_public_network_ip' );
 
+		if ( ! $_ip_address ) {
 			$ip_address = false;
 
-			foreach (self::$providers as $provider_url) {
+			foreach ( self::$providers as $provider_url ) {
+				$response = wp_remote_get(
+					$provider_url,
+					array(
+						'timeout' => 5,
+					)
+				);
 
-				$response = wp_remote_get($provider_url, array(
-					'timeout' => 5,
-				));
-
-				if (!is_wp_error($response)) {
-
-					$ip_address = trim(wp_remote_retrieve_body($response));
+				if ( ! is_wp_error( $response ) ) {
+					$ip_address = trim( wp_remote_retrieve_body( $response ) );
 
 					continue;
-
 				} // end if;
-
 			} // end foreach;
 
-			set_site_transient('wu_public_network_ip', $ip_address, 10 * DAY_IN_SECONDS);
+			set_site_transient( 'wu_public_network_ip', $ip_address, 10 * DAY_IN_SECONDS );
 
 			$_ip_address = $ip_address;
-
 		} // end if;
 
 		/**
@@ -143,10 +135,8 @@ class Helper {
 		 * @param bool $local True if this is a local network (localhost, .dev, etc.), false otherwise.
 		 * @return string The new IP address.
 		 */
-		return apply_filters('wu_get_network_public_ip', $_ip_address, false);
-
+		return apply_filters( 'wu_get_network_public_ip', $_ip_address, false );
 	} // end get_network_public_ip;
-
 	/**
 	 * Checks if a given domain name has a valid associated SSL certificate.
 	 *
@@ -156,24 +146,93 @@ class Helper {
 	 * @return boolean
 	 */
 	public static function has_valid_ssl_certificate($domain = '') {
-
 		$is_valid = false;
 
+		// Ensure the domain is not empty.
+		if (empty($domain)) {
+			return $is_valid;
+		}
+
+		// Add 'https://' if not already present to use SSL context properly.
+		$domain = strpos($domain, 'https://') === 0 ? $domain : 'https://' . $domain;
+
 		try {
+			// Create SSL context to fetch the certificate.
+			$context = stream_context_create(
+				array(
+					'ssl' => array(
+						'capture_peer_cert' => true,
+					),
+				)
+			);
 
-			$certificate = SslCertificate::createForHostName($domain);
+			// Open a stream to the domain over SSL.
+			$stream = @stream_socket_client(
+				'ssl://' . parse_url($domain, PHP_URL_HOST) . ':443',
+				$errno,
+				$errstr,
+				10,
+				STREAM_CLIENT_CONNECT,
+				$context
+			);
 
-			$is_valid = $certificate->isValid($domain); // returns bool;
+			// If stream could not be established, SSL is invalid.
+			if (!$stream) {
+				throw new \Exception($errstr);
+			}
 
+			// Retrieve the certificate and parse its details.
+			$options = stream_context_get_options($context);
+
+			if (isset($options['ssl']['peer_certificate'])) {
+				$cert = openssl_x509_parse($options['ssl']['peer_certificate']);
+
+				if ($cert) {
+					// Verify the certificate's validity period.
+					$current_time = time();
+					$valid_from = $cert['validFrom_time_t'] ?? 0;
+					$valid_to = $cert['validTo_time_t'] ?? 0;
+
+					// Check if the certificate is currently valid.
+					if ($current_time >= $valid_from && $current_time <= $valid_to) {
+						$host = parse_url($domain, PHP_URL_HOST);
+
+						// Check that the domain matches the certificate.
+						$common_name = $cert['subject']['CN'] ?? ''; // Common Name (CN)
+						$alt_names = $cert['extensions']['subjectAltName'] ?? ''; // Subject Alternative Names (SAN)
+
+						// Parse SAN into an array if present.
+						$alt_names_array = array_filter(array_map('trim', explode(',', str_replace('DNS:', '', $alt_names))));
+						$alt_names_array[] = $common_name;
+						// Check if the host matches either the CN, any SAN entry, or supports a wildcard match.
+						if (
+							$host === $common_name ||
+							in_array( $host, $alt_names_array, true )
+						) {
+							$is_valid = true;
+						} else {
+							foreach ($alt_names_array as $alt_name) {
+								if ( strpos($alt_name, '*.') === 0 && str_ends_with( $host, substr($alt_name, 1) )) {
+									$is_valid = true;
+									break;
+								}
+							}
+						}
+					}
+				}
+			}
+
+			// Close the stream after processing.
+			fclose($stream);
 		} catch (\Exception $e) {
-
-			// translators: %s is the error message returned by the checker.
-			wu_log_add('domain-ssl-checks', sprintf(__('Certificate Invalid: %s', 'wp-ultimo'), $e->getMessage()), LogLevel::ERROR);
-
-		} // end try;
+			// Log the error message.
+			wu_log_add(
+				'domain-ssl-checks',
+				sprintf(__('Certificate Invalid: %s', 'wp-ultimo'), $e->getMessage()),
+				LogLevel::ERROR
+			);
+		}
 
 		return $is_valid;
-
 	} // end has_valid_ssl_certificate;
-
 } // end class Helper;
diff --git a/inc/functions/date.php b/inc/functions/date.php
index 32c2577..e101e3a 100644
--- a/inc/functions/date.php
+++ b/inc/functions/date.php
@@ -55,17 +55,15 @@ function wu_validate_date($date, $format = 'Y-m-d H:i:s') {
  * @see https://carbon.nesbot.com/docs/
  *
  * @param string|false $date Parsable date string.
- * @return \Carbon\Carbon
+ * @return \DateTime
  */
 function wu_date($date = false) {
 
 	if (!wu_validate_date($date)) {
-
 		$date = date_i18n('Y-m-d H:i:s');
+	}
 
-	} // end if;
-
-	return \Carbon\Carbon::parse($date);
+	return \DateTime::createFromFormat('Y-m-d H:i:s', $date);
 
 } // end wu_date;
 
@@ -86,7 +84,9 @@ function wu_get_days_ago($date_1, $date_2 = false) {
 
 	$datetime_2 = wu_date($date_2);
 
-	return - $datetime_1->diffInDays($datetime_2, false);
+	$dateIntervar = $datetime_1->diff($datetime_2, false);
+
+	return - $dateIntervar->days;
 
 } // end wu_get_days_ago;
 
diff --git a/inc/installers/class-core-installer.php b/inc/installers/class-core-installer.php
index 5951391..2f67b68 100644
--- a/inc/installers/class-core-installer.php
+++ b/inc/installers/class-core-installer.php
@@ -40,7 +40,7 @@ class Core_Installer extends Base_Installer {
 				if (!(defined('SUNRISE') && SUNRISE)) {
 
 					// translators: %s is a URL to a documentation link.
-					$closte_message = sprintf(__('You are using Closte and they prevent the wp-config.php file from being written to. <a href="%s" target="_blank">Follow these instructions to do it manually</a>.'), wu_get_documentation_url('wp-ultimo-closte-config'));
+					$closte_message = sprintf(__('You are using Closte and they prevent the wp-config.php file from being written to. <a href="%s" target="_blank">Follow these instructions to do it manually</a>.', 'wp-ultimo' ), wu_get_documentation_url('wp-ultimo-closte-config'));
 
 					throw new \Exception($closte_message);
 
diff --git a/inc/installers/class-migrator.php b/inc/installers/class-migrator.php
index f1d68fb..cf9e43b 100644
--- a/inc/installers/class-migrator.php
+++ b/inc/installers/class-migrator.php
@@ -1851,7 +1851,7 @@ class Migrator extends Base_Installer {
 				 */
 				$subscription_creation_date = wu_date($subscription->created_at);
 
-				$trial_end_date = $subscription_creation_date->addDays($subscription->trial)->endOfDay();
+				$trial_end_date = $subscription_creation_date->add( new \DateInterval( 'P' . $subscription->trial . 'D' ) )->setTime( 23, 59, 59 );
 
 				$date_trial_end = $trial_end_date->format('Y-m-d 23:59:59');
 
diff --git a/inc/managers/class-site-manager.php b/inc/managers/class-site-manager.php
index 11cf2e2..b18bcd9 100644
--- a/inc/managers/class-site-manager.php
+++ b/inc/managers/class-site-manager.php
@@ -321,9 +321,9 @@ class Site_Manager extends Base_Manager {
 			// If membership is cancelled we do not add the grace period
 			$grace_period = $status !== Membership_Status::CANCELLED ? (int) wu_get_setting('block_frontend_grace_period', 0) : 0;
 
-			$expiration_time = wu_date($membership->get_date_expiration())->timestamp + $grace_period * DAY_IN_SECONDS;
+			$expiration_time = wu_date($membership->get_date_expiration())->getTimestamp() + $grace_period * DAY_IN_SECONDS;
 
-			if ($expiration_time < wu_date()->timestamp) {
+			if ($expiration_time < wu_date()->getTimestamp()) {
 
 				$checkout_pages = \WP_Ultimo\Checkout\Checkout_Pages::get_instance();
 
diff --git a/inc/models/class-discount-code.php b/inc/models/class-discount-code.php
index 36c0625..1e5bbc1 100644
--- a/inc/models/class-discount-code.php
+++ b/inc/models/class-discount-code.php
@@ -519,6 +519,8 @@ class Discount_Code extends Base_Model {
 
 				return new \WP_Error('discount_code', __('This coupon code is not valid.', 'wp-ultimo'));
 
+				return new \WP_Error( 'discount_code', __( 'The coupon code is not valid yet.', 'wp-ultimo' ) );
+
 			} // end if;
 
 		} // end if;
@@ -527,7 +529,7 @@ class Discount_Code extends Base_Model {
 
 			$expiration_date_instance = wu_date($expiration_date);
 
-			if ($now > $expiration_date) {
+			if ($now > $expiration_date_instance) {
 
 				return new \WP_Error('discount_code', __('This coupon code is not valid.', 'wp-ultimo'));
 
diff --git a/inc/models/class-membership.php b/inc/models/class-membership.php
index 9e741f1..a10485e 100644
--- a/inc/models/class-membership.php
+++ b/inc/models/class-membership.php
@@ -2477,7 +2477,7 @@ class Membership extends Base_Model {
 
 		} // end if;
 
-		return floor($today->diffInDays($expiration_date));
+		return floor($today->diff($expiration_date)->days);
 
 	} // end get_remaining_days_in_cycle;
 
diff --git a/inc/tax/class-dashboard-taxes-tab.php b/inc/tax/class-dashboard-taxes-tab.php
index 8d39e7d..48a1bef 100644
--- a/inc/tax/class-dashboard-taxes-tab.php
+++ b/inc/tax/class-dashboard-taxes-tab.php
@@ -198,15 +198,11 @@ class Dashboard_Taxes_Tab {
 
 		$month_list = array();
 
-		$start = date_i18n('Y-m-d 00:00:00', strtotime('first day of january this year'));
+		$current_year = date_i18n('Y');
 
-		for ($i = 0; $i < 12; $i++) {
-
-			$start_date = wu_date($start);
-
-			$month_list[] = date_i18n('M y', $start_date->addMonths($i)->format('U'));
-
-		} // end for;
+		for ($i = 1; $i <= 12; $i++) {
+			$month_list[] = date_i18n('M y', mktime(0, 0,0,$i,1, $current_year));
+		}
 
 		wp_register_script('wu-tax-stats', wu_get_asset('tax-statistics.js', 'js'), array('jquery', 'wu-functions', 'wu-ajax-list-table', 'moment', 'wu-block-ui', 'dashboard', 'wu-apex-charts', 'wu-vue-apex-charts'), wu_get_version(), true);
 
diff --git a/tests/Admin_Pages/Dashboard_Admin_Page_Test.php b/tests/Admin_Pages/Dashboard_Admin_Page_Test.php
new file mode 100644
index 0000000..8d3bfda
--- /dev/null
+++ b/tests/Admin_Pages/Dashboard_Admin_Page_Test.php
@@ -0,0 +1,45 @@
+<?php
+
+namespace WP_Ultimo\Admin_Pages;
+
+use WP_UnitTestCase;
+
+class Dashboard_Admin_Page_Test extends WP_UnitTestCase {
+
+	/**
+	 * Test the register_scripts method enqueues the necessary scripts and styles.
+	 */
+	public function test_register_scripts() {
+		// Create a mock instance of Dashboard_Admin_Page and call the register_scripts method
+		$dashboard_admin_page = $this->getMockBuilder( Dashboard_Admin_Page::class )
+		                             ->disableOriginalConstructor()
+		                             ->setMethods( [ 'output' ] )
+		                             ->getMock();
+
+		// Fake dates for testing
+		$dashboard_admin_page->start_date = '2023-01-01';
+		$dashboard_admin_page->end_date   = '2023-01-31';
+
+		// Execute register_scripts method
+		$dashboard_admin_page->register_scripts();
+
+		// Assert scripts are registered
+		$this->assertTrue( wp_script_is( 'wu-apex-charts', 'registered' ) );
+		$this->assertTrue( wp_script_is( 'wu-vue-apex-charts', 'registered' ) );
+		$this->assertTrue( wp_script_is( 'wu-dashboard-stats', 'registered' ) );
+
+		// Assert styles are registered
+		$this->assertTrue( wp_style_is( 'wu-apex-charts', 'registered' ) );
+
+		// Assert scripts are enqueued
+		$this->assertTrue( wp_script_is( 'wu-dashboard-stats', 'enqueued' ) );
+
+		// Verify localized script data is correct
+		$localized_vars = wp_scripts()->get_data( 'wu-dashboard-stats', 'data' );
+		echo( $localized_vars );
+		$this->assertStringContainsString( '"month_list":["Jan ', $localized_vars );
+		$this->assertStringContainsString( '"today":"', $localized_vars ); // Check that today is included
+		$this->assertStringContainsString( '"new_mrr":"New MRR"', $localized_vars );
+	}
+
+}
\ No newline at end of file
diff --git a/tests/Admin_Pages/Membership_Edit_Admin_Page_Test.php b/tests/Admin_Pages/Membership_Edit_Admin_Page_Test.php
new file mode 100644
index 0000000..2fb1108
--- /dev/null
+++ b/tests/Admin_Pages/Membership_Edit_Admin_Page_Test.php
@@ -0,0 +1,63 @@
+<?php
+
+namespace WP_Ultimo\Admin_Pages;
+
+use WP_Ultimo\Checkout\Cart;
+use WP_Ultimo\Faker;
+use WP_Ultimo\Models\Membership;
+use WP_UnitTestCase;
+
+/**
+ * Test class for the Membership_Edit_Admin_Page class.
+ *
+ * This class specifically tests the page_loaded method.
+ */
+class Membership_Edit_Admin_Page_Test extends WP_UnitTestCase {
+
+	/**
+	 * Instance of Membership_Edit_Admin_Page.
+	 */
+	protected Membership_Edit_Admin_Page $membership_edit_admin_page;
+
+	protected Membership $membership;
+
+	protected int $swap_time;
+
+	/**
+	 * Sets up the test environment.
+	 */
+	public function setUp(): void {
+		parent::setUp();
+		$faker = new Faker();
+		$faker->generate_fake_memberships();
+		$this->swap_time = strtotime( '+100 days' );
+
+		$this->membership = current( $faker->get_fake_data_generated( 'memberships' ) );
+		$cart             = new Cart( array() );
+		$this->membership->schedule_swap( $cart, gmdate( 'Y-m-d H:i:s', $this->swap_time ) );
+		// Mock Membership_Edit_Admin_Page with dependencies and methods.
+		$this->membership_edit_admin_page = new Membership_Edit_Admin_Page();
+	}
+
+
+	/**
+	 * Tests that page_loaded calls add_swap_notices.
+	 */
+	public function test_page_loaded_calls_add_swap_notices() {
+		$_REQUEST['id'] = $this->membership->get_id();
+		$this->membership_edit_admin_page->page_loaded();
+
+		$membership = $this->membership_edit_admin_page->get_object();
+		$this->assertInstanceOf( Membership::class, $membership );
+		$this->assertEquals( $membership->get_id(), $this->membership->get_id() );
+		$this->assertTrue( $this->membership_edit_admin_page->edit );
+
+		$notices = \WP_Ultimo()->notices->get_notices( 'network-admin' );
+		$this->assertNotEmpty( $notices );
+		$notice = array_shift( $notices );
+		$this->assertEquals( 'warning', $notice['type'] );
+		$this->assertFalse( $notice['dismissible_key'] );
+		$this->assertNotEmpty( $notice['actions'] );
+		$this->assertStringContainsString( gmdate( get_option( 'date_format' ), $this->swap_time ), $notice['message'] );
+	}
+}
diff --git a/tests/WP_Ultimo/Date_Functions_Test.php b/tests/WP_Ultimo/Date_Functions_Test.php
new file mode 100644
index 0000000..dcdf0cd
--- /dev/null
+++ b/tests/WP_Ultimo/Date_Functions_Test.php
@@ -0,0 +1,11 @@
+<?php
+
+namespace WP_Ultimo;
+
+class Date_Functions_Test extends \WP_UnitTestCase {
+	public function test_wu_get_days_ago() {
+		$days = wu_get_days_ago( '2024-01-01 00:00:00', '2024-01-31 00:00:00' );
+
+		$this->assertEquals( -30, $days );
+	}
+}
diff --git a/tests/WP_Ultimo/Models/Discount_Code_Test.php b/tests/WP_Ultimo/Models/Discount_Code_Test.php
new file mode 100644
index 0000000..c8a3eba
--- /dev/null
+++ b/tests/WP_Ultimo/Models/Discount_Code_Test.php
@@ -0,0 +1,128 @@
+<?php
+
+namespace WP_Ultimo\Models;
+
+use WP_Error;
+use WP_UnitTestCase;
+
+class Discount_Code_Test extends WP_UnitTestCase {
+
+	/**
+	 * Tests that a valid discount code returns true.
+	 */
+	public function test_is_valid_active_discount_code() {
+		$discount_code = new Discount_Code();
+		$discount_code->set_active( true );
+
+		$result = $discount_code->is_valid();
+
+		$this->assertTrue( $result );
+	}
+
+	/**
+	 * Tests that an inactive discount code returns an error.
+	 */
+	public function test_is_valid_inactive_discount_code() {
+		$discount_code = new Discount_Code();
+		$discount_code->set_active( false );
+
+		$result = $discount_code->is_valid();
+
+		$this->assertInstanceOf( WP_Error::class, $result );
+		$this->assertEquals( 'discount_code', $result->get_error_code() );
+		$this->assertEquals( 'This coupon code is not valid.', $result->get_error_message() );
+	}
+
+	/**
+	 * Tests that a discount code with max uses returns an error after being used maximum times.
+	 */
+	public function test_is_valid_max_uses_exceeded() {
+		$discount_code = new Discount_Code();
+		$discount_code->set_active( true );
+		$discount_code->set_max_uses( 5 );
+		$discount_code->set_uses( 5 );
+
+		$result = $discount_code->is_valid();
+
+		$this->assertInstanceOf( WP_Error::class, $result );
+		$this->assertEquals( 'discount_code', $result->get_error_code() );
+		$this->assertEquals( 'This discount code was already redeemed the maximum amount of times allowed.',
+			$result->get_error_message() );
+	}
+
+	/**
+	 * Tests that a discount code before the start date is invalid.
+	 */
+	public function test_is_valid_before_start_date() {
+		$discount_code = new Discount_Code();
+		$discount_code->set_active( true );
+		$discount_code->set_date_start( date( 'Y-m-d H:i:s', strtotime( '+1 day' ) ) );
+
+		$result = $discount_code->is_valid();
+
+		$this->assertInstanceOf( WP_Error::class, $result );
+		$this->assertEquals( 'discount_code', $result->get_error_code() );
+		$this->assertEquals( 'This coupon code is not valid.', $result->get_error_message() );
+	}
+
+	/**
+	 * Tests that a discount code after the expiration date is invalid.
+	 */
+	public function test_is_valid_after_expiration_date() {
+		$discount_code = new Discount_Code();
+		$discount_code->set_active( true );
+		$discount_code->set_date_expiration( date( 'Y-m-d H:i:s', strtotime( '-1 day' ) ) );
+
+		$result = $discount_code->is_valid();
+
+		$this->assertInstanceOf( WP_Error::class, $result );
+		$this->assertEquals( 'discount_code', $result->get_error_code() );
+		$this->assertEquals( 'This coupon code is not valid.', $result->get_error_message() );
+	}
+
+	/**
+	 * Tests that a discount code limited to specific products returns true for allowed products.
+	 */
+	public function test_is_valid_for_allowed_product() {
+		$product_id    = 123;
+		$discount_code = new Discount_Code();
+		$discount_code->set_active( true );
+		$discount_code->set_limit_products( true );
+		$discount_code->set_allowed_products( [ $product_id ] );
+
+		$result = $discount_code->is_valid( $product_id );
+
+		$this->assertTrue( $result );
+	}
+
+	/**
+	 * Tests that a discount code limited to specific products returns an error for disallowed products.
+	 */
+	public function test_is_valid_for_disallowed_product() {
+		$allowed_product_id    = 123;
+		$disallowed_product_id = 456;
+		$discount_code         = new Discount_Code();
+		$discount_code->set_active( true );
+		$discount_code->set_limit_products( true );
+		$discount_code->set_allowed_products( [ $allowed_product_id ] );
+
+		$result = $discount_code->is_valid( $disallowed_product_id );
+
+		$this->assertInstanceOf( WP_Error::class, $result );
+		$this->assertEquals( 'discount_code', $result->get_error_code() );
+		$this->assertEquals( 'This coupon code is not valid.', $result->get_error_message() );
+	}
+
+	/**
+	 * Tests that a discount code with no product limits returns true.
+	 */
+	public function test_is_valid_no_product_limits() {
+		$discount_code = new Discount_Code();
+		$discount_code->set_active( true );
+		$discount_code->set_limit_products( false );
+
+		$result = $discount_code->is_valid();
+
+		$this->assertTrue( $result );
+	}
+}
\ No newline at end of file
diff --git a/tests/WP_Ultimo/Models/Domain_Test.php b/tests/WP_Ultimo/Models/Domain_Test.php
new file mode 100644
index 0000000..17be507
--- /dev/null
+++ b/tests/WP_Ultimo/Models/Domain_Test.php
@@ -0,0 +1,44 @@
+<?php
+
+namespace WP_Ultimo\Models;
+
+use WP_UnitTestCase;
+
+class Domain_Test extends WP_UnitTestCase {
+
+	/**
+	 * Test that has_valid_ssl_certificate returns true for valid SSL certificates.
+	 */
+	public function test_has_valid_ssl_certificate_with_valid_certificate() {
+		// Mocking a domain with a valid SSL certificate.
+		$domain = new Domain();
+		$domain->set_domain( 'dogs.4thelols.uk' );
+
+		// Assert that it returns true for a valid SSL certificate.
+		$this->assertTrue( $domain->has_valid_ssl_certificate() );
+	}
+
+	/**
+	 * Test that has_valid_ssl_certificate returns false when the SSL certificate is invalid.
+	 */
+	public function test_has_valid_ssl_certificate_with_invalid_certificate() {
+		// Mocking a domain with an invalid SSL certificate.
+		$domain = new Domain();
+		$domain->set_domain( 'eeeeeeeeeeeeeeeeauauexample.com' );
+
+		// Assert that it returns false for an invalid SSL certificate.
+		$this->assertFalse( $domain->has_valid_ssl_certificate() );
+	}
+
+	/**
+	 * Test that has_valid_ssl_certificate handles empty domain.
+	 */
+	public function test_has_valid_ssl_certificate_with_empty_domain() {
+		// Mocking a domain with an empty value.
+		$domain = new Domain();
+		$domain->set_domain( '' );
+
+		// Assert that it returns false for an empty domain.
+		$this->assertFalse( $domain->has_valid_ssl_certificate() );
+	}
+}
\ No newline at end of file
diff --git a/tests/WP_Ultimo/Models/Membership_Test.php b/tests/WP_Ultimo/Models/Membership_Test.php
new file mode 100644
index 0000000..03bb2a2
--- /dev/null
+++ b/tests/WP_Ultimo/Models/Membership_Test.php
@@ -0,0 +1,173 @@
+<?php
+
+namespace WP_Ultimo\Models;
+
+use WP_Ultimo\Faker;
+
+/**
+ * Unit tests for the Membership class.
+ */
+class Membership_Test extends \WP_UnitTestCase {
+
+	/**
+	 * Membership instance.
+	 *
+	 * @var Membership
+	 */
+	protected $membership;
+
+	/**
+	 * Set up the test environment.
+	 */
+	public function setUp(): void {
+		parent::setUp();
+
+		// Create a new Membership instance for each test.
+		$this->membership = new Membership();
+
+		// Set a default customer ID.
+		$this->membership->set_customer_id( 123 );
+	}
+
+	/**
+	 * Test if the customer is allowed access to the membership.
+	 */
+	public function test_is_customer_allowed() {
+		// Admins with 'manage_network' capability should always return true.
+		$admin_user_id = $this->factory()->user->create( array( 'role' => 'administrator' ) );
+		grant_super_admin( $admin_user_id );
+		wp_set_current_user( $admin_user_id );
+		$this->assertTrue( $this->membership->is_customer_allowed(), 'Failed asserting that admin is allowed.' );
+
+		// Regular customers are allowed if IDs match.
+		$customer_id = 123;
+		$this->assertTrue(
+			$this->membership->is_customer_allowed( $customer_id ),
+			'Failed asserting that customer with matching ID is allowed.'
+		);
+
+		// Regular customers are denied if IDs do not match.
+		$wrong_customer_id = 456;
+		wp_set_current_user( $wrong_customer_id );
+		$this->assertFalse(
+			$this->membership->is_customer_allowed( $wrong_customer_id ),
+			'Failed asserting that customer with non-matching ID is denied.'
+		);
+	}
+
+	/**
+	 * Test adding a product to the membership.
+	 */
+	public function test_add_product() {
+		// Add a product with a specific ID and quantity.
+		$quantity = 2;
+		$faker    = new Faker();
+		$faker->generate_fake_products();
+		/** @var Product $product */
+		$product    = $faker->get_fake_data_generated( 'products' )[0];
+		$product_id = $product->get_id();
+
+		$this->membership->add_product( $product_id, $quantity );
+
+		// Verify that the product is added with the correct quantity.
+		$addon_products = $this->membership->get_addon_ids();
+		$this->assertContains( $product_id, $addon_products, 'Failed asserting that product ID was added.' );
+		$this->assertEquals(
+			$quantity,
+			$this->membership->get_addon_products()[0]['quantity'],
+			'Failed asserting that the product quantity is correct.'
+		);
+
+		// Add more of the same product and check the updated quantity.
+		$additional_quantity = 3;
+		$this->membership->add_product( $product_id, $additional_quantity );
+
+		$this->assertEquals(
+			$quantity + $additional_quantity,
+			$this->membership->get_addon_products()[0]['quantity'],
+			'Failed asserting that the quantity was updated correctly for the same product.'
+		);
+	}
+
+	/**
+	 * Test removing a product from the membership.
+	 */
+	public function test_remove_product() {
+		// Add a product with a specific quantity.
+		$quantity = 5;
+		$faker    = new Faker();
+		$faker->generate_fake_products();
+		/** @var Product $product */
+		$product    = $faker->get_fake_data_generated( 'products' )[0];
+		$product_id = $product->get_id();
+
+		$this->membership->add_product( $product_id, $quantity );
+
+		// Remove some of the product's quantity.
+		$remove_quantity = 3;
+		$this->membership->remove_product( $product_id, $remove_quantity );
+
+		// Verify the updated quantity.
+		$this->assertEquals(
+			$quantity - $remove_quantity,
+			$this->membership->get_addon_products()[0]['quantity'],
+			'Failed asserting that the quantity was reduced correctly.'
+		);
+
+		// Remove the remaining quantity and verify it is removed.
+		$this->membership->remove_product( $product_id, $quantity );
+		$addon_products = $this->membership->get_addon_ids();
+		$this->assertNotContains( $product_id, $addon_products, 'Failed asserting that the product was removed.' );
+	}
+
+	/**
+	 * Test get_remaining_days_in_cycle() method.
+	 */
+	public function test_get_remaining_days_in_cycle() {
+		$this->membership->set_amount( 12.99 );
+		// Case 1: Non-recurring membership should return 10000.
+		$this->membership->set_recurring( false );
+		$this->assertEquals(
+			10000,
+			$this->membership->get_remaining_days_in_cycle(),
+			'Failed asserting that non-recurring membership returns 10000.'
+		);
+
+		// Case 2: Invalid expiration date should return 0.
+		$this->membership->set_recurring( true );
+		$this->membership->set_date_expiration( 'invalid-date' ); // Setting an invalid date.
+		$this->assertEquals(
+			0,
+			$this->membership->get_remaining_days_in_cycle(),
+			'Failed asserting that an invalid expiration date returns 0.'
+		);
+
+		// Case 3: No expiration date should return 0.
+		$this->membership->set_date_expiration( '' );
+		$this->assertEquals(
+			0,
+			$this->membership->get_remaining_days_in_cycle(),
+			'Failed asserting that no expiration date returns 0.'
+		);
+
+		// Case 4: Expiration date is in the future and remaining days are calculated properly.
+		$today = new \DateTime( 'now', new \DateTimeZone( 'UTC' ) );
+		$today->add( new \DateInterval( 'P10D' ) );
+		$this->membership->set_date_expiration( $today->format( 'Y-m-d H:i:s' ) );
+		$remaining_days = $this->membership->get_remaining_days_in_cycle();
+		$this->assertEquals(
+			10,
+			$remaining_days,
+			'Failed asserting that 10 days remain when expiration date is 10 days in the future.'
+		);
+
+		// Case 5: Expiration date is in the past, should return 0.
+		$this->membership->set_date_expiration( date( 'Y-m-d H:i:s', strtotime( '-5 days' ) ) );
+		$remaining_days = $this->membership->get_remaining_days_in_cycle();
+		$this->assertEquals(
+			0,
+			$remaining_days,
+			'Failed asserting that remaining days return 0 when the expiration date is in the past.'
+		);
+	}
+}
diff --git a/tests/WP_Ultimo/Tax/Dashboard_Taxes_Tab_Test.php b/tests/WP_Ultimo/Tax/Dashboard_Taxes_Tab_Test.php
new file mode 100644
index 0000000..0f031ca
--- /dev/null
+++ b/tests/WP_Ultimo/Tax/Dashboard_Taxes_Tab_Test.php
@@ -0,0 +1,34 @@
+<?php
+
+namespace WP_Ultimo\Tax;
+
+use WP_UnitTestCase;
+
+class Dashboard_Taxes_Tab_Test extends WP_UnitTestCase {
+
+	/**
+	 * Test that register_scripts method registers the correct scripts.
+	 */
+	public function test_register_scripts_registers_scripts() {
+		// Create a mock instance of Dashboard_Admin_Page and call the register_scripts method.
+		$dashboard_admin_page = $this->getMockBuilder( Dashboard_Taxes_Tab::class )
+									->disableOriginalConstructor()
+									->setMethods( array( 'output' ) )
+									->getMock();
+
+		// Execute register_scripts method.
+		$dashboard_admin_page->register_scripts();
+
+		// Assert scripts are registered.
+		$this->assertTrue( wp_script_is( 'wu-tax-stats', 'registered' ) );
+
+		// Assert scripts are enqueued.
+		$this->assertTrue( wp_script_is( 'wu-tax-stats', 'enqueued' ) );
+
+		// Verify localized script data is correct.
+		$localized_vars = wp_scripts()->get_data( 'wu-tax-stats', 'data' );
+		$this->assertStringContainsString( '"month_list":["Jan ', $localized_vars );
+		$this->assertStringContainsString( '"today":"', $localized_vars ); // Check that today is included.
+		$this->assertStringContainsString( '"net_profit_label":"Net Profit"', $localized_vars );
+	}
+}