[update] combine union test in single class

tests/Model/Client.php

@@ -7,7 +7,7 @@
 class Client extends User
 {
     public $table = 'client';
-    
+
     public function init(): void
     {
         parent::init();

tests/Model/Payment.php

@@ -5,7 +5,6 @@
 namespace atk4\data\tests\Model;
 
 use atk4\data\Model;
-use atk4\data\tests\Model\Client;
 
 class Payment extends Model
 {

tests/Model/Transaction.php

@@ -10,13 +10,15 @@ class Transaction extends Union
 {
     public $nestedInvoice;
     public $nestedPayment;
-
+
+    public $subtractInvoice;
+
     public function init(): void
     {
         parent::init();
 
         // first lets define nested models
-        $this->nestedInvoice = $this->addNestedModel(new Invoice());
+        $this->nestedInvoice = $this->addNestedModel(new Invoice(), $this->subtractInvoice ? ['amount' => '-[]'] : []);
         $this->nestedPayment = $this->addNestedModel(new Payment());
 
         // next, define common fields

tests/ModelAggregateTest.php

@@ -34,10 +34,10 @@ protected function setUp(): void
         parent::setUp();
         $this->setDB($this->init_db);
 
-        $m_invoice = new Model\Invoice($this->db);
-        $m_invoice->getRef('client_id')->addTitle();
+        $invoice = new Model\Invoice($this->db);
+        $invoice->getRef('client_id')->addTitle();
 
-        $this->aggregate = new Aggregate($m_invoice);
+        $this->aggregate = new Aggregate($invoice);
         $this->aggregate->addField('client');
     }