fix: Add exception message in callback message (#106)

* fix: Add exception message in callback message

Author: izaaz

src/main/java/com/amplitude/HttpTransport.java

@@ -434,6 +434,8 @@ public void run() {
           callbackMessage = "Unknown response status.";
         }
       } catch (Exception exception) {
+        callbackMessage =
+                "Error sending events due to the exception: " + exception + ". Message: " + exception.getMessage();
         logger.error("Flush Thread Error", Utils.getStackTrace(exception));
         logger.error("Error event payload", events.toString());
       } finally {

src/test/java/com/amplitude/HttpTransportTest.java

@@ -435,7 +435,7 @@ public void testThreadTimeoutCallback()
           @Override
           public void onLogEventServerResponse(Event event, int status, String message) {
             resultMap.put(event, status);
-            assertEquals("Error send events", message);
+            assertEquals("Error sending events due to the exception: java.util.concurrent.TimeoutException. Message: null", message);
             latch.countDown();
           }
         };