Calculation errors for refunded amounts

tests/Feature/InvoiceTypeSelectionTest.php

@@ -90,4 +90,16 @@ class InvoiceTypeSelectionTest extends TestCase
             InvoiceType::selectable()->pluck('slug')->all()
         );
     }
+
+    public function test_the_refund_type_does_not_count_as_an_expense(): void
+    {
+        // Sie mindert die Einnahmenseite bereits -- als Ausgabe gezählt, stünde sie zweimal in der Bilanz.
+        $this->assertSame(
+            [InvoiceType::INVOICE_TYPE_PROGRAM, InvoiceType::INVOICE_TYPE_OTHER],
+            InvoiceType::countingAsExpense()->pluck('slug')->all()
+        );
+
+        $type = InvoiceType::where('slug', InvoiceType::INVOICE_TYPE_PARTICIPATION_REFUND)->first();
+        $this->assertFalse($type->counts_as_expense);
+    }
 }