refactor the spring boot persistence mongodb module (#5829)

* added example code for BAEL-2366

* moved example code for BAEL-2366

* example code for BAEL-1961

* moved example code into integration test

* updated the test assertions

* refactor the spring boot persistence mongodb module

* remove redundant example code

* declared the spring boot persistence module in the root pom

* fixed issue with non-imported file

persistence-modules/spring-boot-persistence-mongodb/src/test/java/com/baeldung/mongodb/MongoDbAutoGeneratedFieldIntegrationTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.mongodb;
+
+import com.baeldung.mongodb.daos.UserRepository;
+import com.baeldung.mongodb.models.User;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit4.SpringRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+
+@RunWith(SpringRunner.class)
+@SpringBootTest
+public class MongoDbAutoGeneratedFieldIntegrationTest {
+
+    @Autowired
+    UserRepository userRepository;
+
+    @Test
+    public void contextLoads() {}
+
+    @Test
+    public void givenUserObject_whenSave_thenCreateNewUser() {
+
+        User user = new User();
+        user.setFirstName("John");
+        user.setLastName("Doe");
+        user.setEmail("john.doe@example.com");
+        userRepository.save(user);
+
+        assertThat(userRepository.findAll().size()).isGreaterThan(0);
+    }
+
+
+}