fix: flaky unit tests (#1253)

Author: csviri

operator-framework-core/src/test/java/io/javaoperatorsdk/operator/processing/event/EventProcessorTest.java

@@ -116,7 +116,11 @@ void executesTheControllerInstantlyAfterErrorIfNewEventsReceived() {
         PostExecutionControl.exceptionDuringExecution(new RuntimeException("test"));
 
     when(reconciliationDispatcherMock.handleExecution(any()))
-        .thenReturn(postExecutionControl)
+        .thenAnswer((Answer<PostExecutionControl>) invocationOnMock -> {
+          // avoid to process the first event before the second submitted
+          Thread.sleep(50);
+          return postExecutionControl;
+        })
         .thenReturn(PostExecutionControl.defaultDispatch());
 
     // start processing an event