feat: Idempotent Consumer Microservice Pattern #2683 (#3082)

* added idempotent consumer pattern

* updated doc

* fixed bug in RequestService

* add test converage

* Add test converage to state machine

* renamed module and added code example

microservices-idempotent-consumer/src/test/java/com/iluwatar/idempotentconsumer/AppTest.java

@@ -0,0 +1,46 @@
+package com.iluwatar.idempotentconsumer;
+
+import org.junit.jupiter.api.Test;
+import org.mockito.Mockito;
+import org.springframework.boot.CommandLineRunner;
+
+import java.util.UUID;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+/**
+ * Application test
+ */
+class AppTest {
+
+  @Test
+  void main() {
+    assertDoesNotThrow(() -> App.main(new String[] {}));
+  }
+
+  @Test
+  void run() throws Exception {
+    RequestService requestService = Mockito.mock(RequestService.class);
+    RequestRepository requestRepository = Mockito.mock(RequestRepository.class);
+    UUID uuid = UUID.randomUUID();
+    Request requestPending = new Request(uuid);
+    Request requestStarted = new Request(uuid, Request.Status.STARTED);
+    Request requestCompleted = new Request(uuid, Request.Status.COMPLETED);
+    when(requestService.create(any())).thenReturn(requestPending);
+    when(requestService.start(any())).thenReturn(requestStarted);
+    when(requestService.complete(any())).thenReturn(requestCompleted);
+
+    CommandLineRunner runner = new App().run(requestService, requestRepository);
+
+    runner.run();
+
+    verify(requestService, times(3)).create(any());
+    verify(requestService, times(2)).start(any());
+    verify(requestService, times(1)).complete(any());
+    verify(requestRepository, times(1)).count();
+  }
+}