added code snippets for bael-4554 (#9979)

testing-modules/mockito-2/src/main/java/com/baeldung/mockito/whenvsdomethods/Employee.java

@@ -0,0 +1,11 @@
+package com.baeldung.mockito.whenvsdomethods;
+
+import java.time.DayOfWeek;
+
+public interface Employee {
+
+    String greet();
+    
+    void work(DayOfWeek day);
+    
+}

testing-modules/mockito-2/src/main/java/com/baeldung/mockito/whenvsdomethods/IAmOnHolidayException.java

@@ -0,0 +1,5 @@
+package com.baeldung.mockito.whenvsdomethods;
+
+public class IAmOnHolidayException extends RuntimeException {
+
+}