diff --git a/tests/Http/SendInvoicesTest.php b/tests/Http/SendInvoicesTest.php
index de27be7..72ef263 100644
--- a/tests/Http/SendInvoicesTest.php
+++ b/tests/Http/SendInvoicesTest.php
@@ -3,6 +3,7 @@
 namespace Tests\Http;
 
 use Firebed\AadeMyData\Exceptions\MyDataException;
+use Firebed\AadeMyData\Exceptions\TransmissionFailedException;
 use Firebed\AadeMyData\Factories\ResponseDocXmlFactory;
 use Firebed\AadeMyData\Http\MyDataRequest;
 use Firebed\AadeMyData\Http\SendInvoices;
@@ -34,14 +35,14 @@ public function test_dev_provider_url_is_correct()
         $sendInvoices = new SendInvoices();
         $this->assertEquals('https://mydataapidev.aade.gr/myDataProvider/SendInvoices', $sendInvoices->getUrl());
     }
-    
+
     public function test_prod_provider_url_is_correct()
     {
         MyDataRequest::init('test_user_id', 'test_user_secret', 'prod', true);
         $sendInvoices = new SendInvoices();
         $this->assertEquals('https://mydatapi.aade.gr/myDataProvider/SendInvoices', $sendInvoices->getUrl());
-    }    
-    
+    }
+
     /**
      * @throws MyDataException
      */
@@ -59,7 +60,7 @@ public function test_it_sends_single_invoice()
 
         $this->assertCount(1, $responseDoc);
     }
-    
+
     /**
      * @throws MyDataException
      */
@@ -126,4 +127,19 @@ public function test_it_sends_a_single_invoice()
 
         $this->assertCount(1, $responseDoc);
     }
+
+    /**
+     * @throws MyDataException
+     */
+    public function test_transmission_failure_throws_exception()
+    {
+        MyDataRequest::setHandler(new MockHandler([
+            new HttpResponse(500),
+        ]));
+
+        $this->expectException(TransmissionFailedException::class);
+
+        $sendInvoices = new SendInvoices();
+        $sendInvoices->handle(new Invoice());
+    }
 }
\ No newline at end of file
diff --git a/tests/InvoiceTest.php b/tests/InvoiceTest.php
index b15cc84..9aeae03 100644
--- a/tests/InvoiceTest.php
+++ b/tests/InvoiceTest.php
@@ -28,7 +28,7 @@ public function test_invoice_xml()
                 ]
             ]
         ]);
-            
+
         $invoice = Invoice::factory()->make();
         $this->assertNotEmpty($invoice->toXml());
     }
@@ -54,13 +54,13 @@ public function test_invoice_validation()
         $invoice = Invoice::factory()->make();
         $this->assertEmpty($invoice->validate());
     }
-    
+
     public function test_invoice_validation_fail()
     {
         $invoice = Invoice::factory()->make();
         $invoice->getInvoiceHeader()->setInvoiceType("wrong");
         $invoice->getInvoiceSummary()->setTotalGrossValue(-10);
-        
+
         // "wrong" value will be cast to null because InvoiceType enum does
         // not have "wrong" value.
         // Since null values are stripped from the array, we expect a failure