diff --git a/plugins/woocommerce/tests/php/src/Database/Migrations/CustomOrderTable/WPPostToCOTMigratorTest.php b/plugins/woocommerce/tests/php/src/Database/Migrations/CustomOrderTable/WPPostToCOTMigratorTest.php
index 57d7868b06d..4de5d1cfce6 100644
--- a/plugins/woocommerce/tests/php/src/Database/Migrations/CustomOrderTable/WPPostToCOTMigratorTest.php
+++ b/plugins/woocommerce/tests/php/src/Database/Migrations/CustomOrderTable/WPPostToCOTMigratorTest.php
@@ -35,136 +35,113 @@ class WPPostToCOTMigratorTest extends \WC_Unit_Test_Case {
 		parent::setUp();
 		$this->create_order_custom_table_if_not_exist();
 		$this->data_store = wc_get_container()->get( OrdersTableDataStore::class );
-		$this->sut = wc_get_container()->get( WPPostToCOTMigrator::class );
+		$this->sut        = wc_get_container()->get( WPPostToCOTMigrator::class );
 	}
 
 	public function test_process_next_migration_batch_normal_order() {
-
 		$order = wc_get_order( $this->create_complex_wp_post_order() );
 		$this->clear_all_orders_and_reset_checkpoint();
 		$this->sut->process_next_migration_batch( 100 );
-		$db_order = $this->get_order_from_cot( $order );
-
-		// Verify core data.
-		$this->assertEquals( $order->get_id(), $db_order->post_id );
-		$this->assertEquals( 'wc-' . $order->get_status(), $db_order->status );
-		$this->assertEquals( 'INR', $db_order->currency );
-		$this->assertEquals( $order->get_customer_id(), $db_order->customer_id );
-		$this->assertEquals( $order->get_billing_email(), $db_order->billing_email );
-		$this->assertEquals( $order->get_payment_method(), $db_order->payment_method );
-		$this->assertEquals(
-			$order->get_date_created()->date( DATE_ISO8601 ),
-			( new WC_DateTime( $db_order->date_created_gmt ) )->date( DATE_ISO8601 )
-		);
-		$this->assertEquals( $order->get_date_modified()->date( DATE_ISO8601 ), ( new WC_DateTime( $db_order->date_updated_gmt ) )->date( DATE_ISO8601 ) );
-		$this->assertEquals( $order->get_parent_id(), $db_order->parent_order_id );
-		$this->assertEquals( $order->get_payment_method_title(), $db_order->payment_method_title );
-		$this->assertEquals( $order->get_transaction_id(), $db_order->transaction_id );
-		$this->assertEquals( $order->get_customer_ip_address(), $db_order->ip_address );
-		$this->assertEquals( $order->get_customer_user_agent(), $db_order->user_agent );
-
-		// Verify order billing address.
-		$db_order_address = $this->get_address_details_from_cot( $db_order->id, 'billing' );
-		$this->assertEquals( $order->get_billing_first_name(), $db_order_address->first_name );
-		$this->assertEquals( $order->get_billing_last_name(), $db_order_address->last_name );
-		$this->assertEquals( $order->get_billing_company(), $db_order_address->company );
-		$this->assertEquals( $order->get_billing_address_1(), $db_order_address->address_1 );
-		$this->assertEquals( $order->get_billing_address_2(), $db_order_address->address_2 );
-		$this->assertEquals( $order->get_billing_city(), $db_order_address->city );
-		$this->assertEquals( $order->get_billing_postcode(), $db_order_address->postcode );
-		$this->assertEquals( $order->get_billing_country(), $db_order_address->country );
-		$this->assertEquals( $order->get_billing_email(), $db_order_address->email );
-		$this->assertEquals( $order->get_billing_phone(), $db_order_address->phone );
-
-		// Verify order shipping address.
-		$db_order_address = $this->get_address_details_from_cot( $db_order->id, 'shipping' );
-		$this->assertEquals( $order->get_shipping_first_name(), $db_order_address->first_name );
-		$this->assertEquals( $order->get_shipping_last_name(), $db_order_address->last_name );
-		$this->assertEquals( $order->get_shipping_company(), $db_order_address->company );
-		$this->assertEquals( $order->get_shipping_address_1(), $db_order_address->address_1 );
-		$this->assertEquals( $order->get_shipping_address_2(), $db_order_address->address_2 );
-		$this->assertEquals( $order->get_shipping_city(), $db_order_address->city );
-		$this->assertEquals( $order->get_shipping_postcode(), $db_order_address->postcode );
-		$this->assertEquals( $order->get_shipping_country(), $db_order_address->country );
-		$this->assertEquals( $order->get_shipping_phone(), $db_order_address->phone );
-
-		// Verify order operational data.
-		$db_order_op_data = $this->get_order_operational_data_from_cot( $db_order->id );
-		$this->assertEquals( $order->get_created_via(), $db_order_op_data->created_via );
-		$this->assertEquals( $order->get_version(), $db_order_op_data->woocommerce_version );
-		$this->assertEquals( $order->get_prices_include_tax(), $db_order_op_data->prices_include_tax );
-		$this->assertEquals(
-			wc_string_to_bool( $order->get_data_store()->get_recorded_coupon_usage_counts( $order ) ),
-			$db_order_op_data->coupon_usages_are_counted
-		);
-		$this->assertEquals(
-			wc_string_to_bool( $order->get_data_store()->get_download_permissions_granted( $order ) ),
-			$db_order_op_data->download_permission_granted
-		);
-		$this->assertEquals( $order->get_cart_hash(), $db_order_op_data->cart_hash );
-		$this->assertEquals(
-			wc_string_to_bool( $order->get_meta( '_new_order_email_sent' ) ),
-			$db_order_op_data->new_order_email_sent
-		);
-		$this->assertEquals( $order->get_order_key(), $db_order_op_data->order_key );
-		$this->assertEquals( $order->get_data_store()->get_stock_reduced( $order ), $db_order_op_data->order_stock_reduced );
-		$this->assertEquals(
-			$order->get_date_paid()->date( DATE_ISO8601 ),
-			( new WC_DateTime( $db_order_op_data->date_paid_gmt ) )->date( DATE_ISO8601 )
-		);
-		$this->assertEquals(
-			$order->get_date_completed()->date( DATE_ISO8601 ),
-			( new WC_DateTime( $db_order_op_data->date_completed_gmt ) )->date( DATE_ISO8601 )
-		);
-		$this->assertEquals( $order->get_shipping_tax(), $db_order_op_data->shipping_tax_amount );
-		$this->assertEquals( $order->get_shipping_total(), $db_order_op_data->shipping_total_amount );
-		$this->assertEquals( $order->get_discount_tax(), $db_order_op_data->discount_tax_amount );
-		$this->assertEquals( $order->get_discount_total(), $db_order_op_data->discount_total_amount );
-	}
-
-	public function test_process_next_migration_batch_interrupted_migrating_order() {
 
+		$this->assert_core_data_is_migrated( $order );
+		$this->assert_order_addresses_are_migrated( $order );
+		$this->assert_order_op_data_is_migrated( $order );
 	}
 
 	public function test_process_next_migration_batch_already_migrated_order() {
+		global $wpdb;
+		$order = wc_get_order( $this->create_complex_wp_post_order() );
+		$this->clear_all_orders_and_reset_checkpoint();
 
+		// Run the migration once.
+		$this->sut->process_next_migration_batch( 100 );
+
+		// Delete checkpoint and run migration again, assert there are still no duplicates.
+		$this->sut->update_checkpoint( 0 );
+		$this->sut->process_next_migration_batch( 100 );
+
+		$this->assertEquals(
+			1,
+			$wpdb->get_var(
+				"
+SELECT COUNT(*) FROM {$this->data_store::get_orders_table_name()}
+WHERE post_id = {$order->get_id()}"
+			),
+			'Order record is duplicated.'
+		);
+		$order_id = $wpdb->get_var( "SELECT id FROM {$this->data_store::get_orders_table_name()} WHERE post_id = {$order->get_id()}" );
+		$this->assertEquals(
+			1,
+			$wpdb->get_var(
+				"
+SELECT COUNT(*) FROM {$this->data_store::get_addresses_table_name()}
+WHERE order_id = {$order_id} AND address_type = 'billing'
+"
+			)
+		);
+		$this->assertEquals(
+			1,
+			$wpdb->get_var(
+				"
+SELECT COUNT(*) FROM {$this->data_store::get_addresses_table_name()}
+WHERE order_id = {$order_id} AND address_type = 'shipping'
+"
+			)
+		);
+		$this->assertEquals(
+			1,
+			$wpdb->get_var(
+				"
+SELECT COUNT(*) FROM {$this->data_store::get_operational_data_table_name()}
+WHERE order_id = {$order_id}
+"
+			)
+		);
+	}
+
+	public function test_process_next_migration_batch_interrupted_migrating_order() {
+		$this->markTestSkipped();
 	}
 
 	public function test_process_next_migration_batch_invalid_order_data() {
-
+		$this->markTestSkipped();
 	}
 
 	public function test_process_next_migration_batch_invalid_valid_order_combo() {
-
+		$this->markTestSkipped();
 	}
 
 	public function test_process_next_migration_batch_stale_order() {
-
+		$this->markTestSkipped();
 	}
 
 	private function get_order_from_cot( $post_order ) {
 		global $wpdb;
 		$order_table = $this->data_store::get_orders_table_name();
-		$query = "SELECT * FROM $order_table WHERE post_id = {$post_order->get_id()};";
+		$query       = "SELECT * FROM $order_table WHERE post_id = {$post_order->get_id()};";
+
 		return $wpdb->get_row( $query );
 	}
 
 	private function get_address_details_from_cot( $order_id, $address_type ) {
 		global $wpdb;
 		$address_table = $this->data_store::get_addresses_table_name();
+
 		return $wpdb->get_row( "SELECT * FROM $address_table WHERE order_id = $order_id AND address_type = '$address_type';" );
 	}
 
 	private function get_order_operational_data_from_cot( $order_id ) {
 		global $wpdb;
 		$operational_data_table = $this->data_store::get_operational_data_table_name();
+
 		return $wpdb->get_row( "SELECT * FROM $operational_data_table WHERE order_id = $order_id;" );
 	}
 
 	private function create_complex_wp_post_order() {
 		update_option( 'woocommerce_prices_include_tax', 'yes' );
 		update_option( 'woocommerce_calc_taxes', 'yes' );
-		$customer = CustomerHelper::create_customer();
+		$uniq_cust_id = wp_generate_password( 10, false );
+		$customer = CustomerHelper::create_customer( "user$uniq_cust_id", $uniq_cust_id, "user$uniq_cust_id@example.com" );
 		$tax_rate = array(
 			'tax_rate_country'  => '',
 			'tax_rate_state'    => '',
@@ -228,6 +205,93 @@ class WPPostToCOTMigratorTest extends \WC_Unit_Test_Case {
 		return $order->get_id();
 	}
 
+	private function assert_core_data_is_migrated( $order ) {
+		$db_order = $this->get_order_from_cot( $order );
+
+		// Verify core data.
+		$this->assertEquals( $order->get_id(), $db_order->post_id );
+		$this->assertEquals( 'wc-' . $order->get_status(), $db_order->status );
+		$this->assertEquals( 'INR', $db_order->currency );
+		$this->assertEquals( $order->get_customer_id(), $db_order->customer_id );
+		$this->assertEquals( $order->get_billing_email(), $db_order->billing_email );
+		$this->assertEquals( $order->get_payment_method(), $db_order->payment_method );
+		$this->assertEquals(
+			$order->get_date_created()->date( DATE_ISO8601 ),
+			( new WC_DateTime( $db_order->date_created_gmt ) )->date( DATE_ISO8601 )
+		);
+		$this->assertEquals( $order->get_date_modified()->date( DATE_ISO8601 ), ( new WC_DateTime( $db_order->date_updated_gmt ) )->date( DATE_ISO8601 ) );
+		$this->assertEquals( $order->get_parent_id(), $db_order->parent_order_id );
+		$this->assertEquals( $order->get_payment_method_title(), $db_order->payment_method_title );
+		$this->assertEquals( $order->get_transaction_id(), $db_order->transaction_id );
+		$this->assertEquals( $order->get_customer_ip_address(), $db_order->ip_address );
+		$this->assertEquals( $order->get_customer_user_agent(), $db_order->user_agent );
+	}
+
+	private function assert_order_addresses_are_migrated( $order ) {
+		$db_order = $this->get_order_from_cot( $order );
+
+		// Verify order billing address.
+		$db_order_address = $this->get_address_details_from_cot( $db_order->id, 'billing' );
+		$this->assertEquals( $order->get_billing_first_name(), $db_order_address->first_name );
+		$this->assertEquals( $order->get_billing_last_name(), $db_order_address->last_name );
+		$this->assertEquals( $order->get_billing_company(), $db_order_address->company );
+		$this->assertEquals( $order->get_billing_address_1(), $db_order_address->address_1 );
+		$this->assertEquals( $order->get_billing_address_2(), $db_order_address->address_2 );
+		$this->assertEquals( $order->get_billing_city(), $db_order_address->city );
+		$this->assertEquals( $order->get_billing_postcode(), $db_order_address->postcode );
+		$this->assertEquals( $order->get_billing_country(), $db_order_address->country );
+		$this->assertEquals( $order->get_billing_email(), $db_order_address->email );
+		$this->assertEquals( $order->get_billing_phone(), $db_order_address->phone );
+
+		// Verify order shipping address.
+		$db_order_address = $this->get_address_details_from_cot( $db_order->id, 'shipping' );
+		$this->assertEquals( $order->get_shipping_first_name(), $db_order_address->first_name );
+		$this->assertEquals( $order->get_shipping_last_name(), $db_order_address->last_name );
+		$this->assertEquals( $order->get_shipping_company(), $db_order_address->company );
+		$this->assertEquals( $order->get_shipping_address_1(), $db_order_address->address_1 );
+		$this->assertEquals( $order->get_shipping_address_2(), $db_order_address->address_2 );
+		$this->assertEquals( $order->get_shipping_city(), $db_order_address->city );
+		$this->assertEquals( $order->get_shipping_postcode(), $db_order_address->postcode );
+		$this->assertEquals( $order->get_shipping_country(), $db_order_address->country );
+		$this->assertEquals( $order->get_shipping_phone(), $db_order_address->phone );
+	}
+
+	private function assert_order_op_data_is_migrated( $order ) {
+		$db_order = $this->get_order_from_cot( $order );
+		// Verify order operational data.
+		$db_order_op_data = $this->get_order_operational_data_from_cot( $db_order->id );
+		$this->assertEquals( $order->get_created_via(), $db_order_op_data->created_via );
+		$this->assertEquals( $order->get_version(), $db_order_op_data->woocommerce_version );
+		$this->assertEquals( $order->get_prices_include_tax(), $db_order_op_data->prices_include_tax );
+		$this->assertEquals(
+			wc_string_to_bool( $order->get_data_store()->get_recorded_coupon_usage_counts( $order ) ),
+			$db_order_op_data->coupon_usages_are_counted
+		);
+		$this->assertEquals(
+			wc_string_to_bool( $order->get_data_store()->get_download_permissions_granted( $order ) ),
+			$db_order_op_data->download_permission_granted
+		);
+		$this->assertEquals( $order->get_cart_hash(), $db_order_op_data->cart_hash );
+		$this->assertEquals(
+			wc_string_to_bool( $order->get_meta( '_new_order_email_sent' ) ),
+			$db_order_op_data->new_order_email_sent
+		);
+		$this->assertEquals( $order->get_order_key(), $db_order_op_data->order_key );
+		$this->assertEquals( $order->get_data_store()->get_stock_reduced( $order ), $db_order_op_data->order_stock_reduced );
+		$this->assertEquals(
+			$order->get_date_paid()->date( DATE_ISO8601 ),
+			( new WC_DateTime( $db_order_op_data->date_paid_gmt ) )->date( DATE_ISO8601 )
+		);
+		$this->assertEquals(
+			$order->get_date_completed()->date( DATE_ISO8601 ),
+			( new WC_DateTime( $db_order_op_data->date_completed_gmt ) )->date( DATE_ISO8601 )
+		);
+		$this->assertEquals( $order->get_shipping_tax(), $db_order_op_data->shipping_tax_amount );
+		$this->assertEquals( $order->get_shipping_total(), $db_order_op_data->shipping_total_amount );
+		$this->assertEquals( $order->get_discount_tax(), $db_order_op_data->discount_tax_amount );
+		$this->assertEquals( $order->get_discount_total(), $db_order_op_data->discount_total_amount );
+	}
+
 	private function clear_all_orders_and_reset_checkpoint() {
 		global $wpdb;
 		$order_tables = $this->data_store->get_all_table_names();
@@ -243,7 +307,7 @@ class WPPostToCOTMigratorTest extends \WC_Unit_Test_Case {
 		$order_table_controller->show_feature();
 		$this->synchronizer = wc_get_container()
 			->get( DataSynchronizer::class );
-		if( ! $this->synchronizer->check_orders_table_exists() ) {
+		if ( ! $this->synchronizer->check_orders_table_exists() ) {
 			$this->synchronizer->create_database_tables();
 		}
 	}