Use in-memory db to write tests for Rest controllers

Remove both annotations @AutoConfigureMockMvc and @DataJpaTest. You are trying to test the complete applciation, so need the @SpringBootTest annotation. @DataJpaTest is only needed if you want to test only the data apllication slice. Have a look at this: https://spring.io/blog/2016/04/15/testing-improvements-in-spring-boot-1-4

For Testing REST service with in-memory DB, you need to following things:
1. Add h2 dependency in pom.xml

<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
    <scope>runtime</scope>
    <optional>true</optional>
</dependency>

2. Define h2 configuration in application.properties or application.yaml

spring.jpa.database = h2
spring.datasource.url=jdbc:hsqldb:mem:testdb
spring.datasource.username=sa
spring.datasource.password=
spring.jpa.database-platform=org.hibernate.dialect.HSQLDialect
spring.jpa.show-sql=true
spring.jpa.hibernate.ddl-auto=create

3. Annotate you test class

@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)

Complete code will be like:

@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class AuthenticationControllerFTest {

    @Autowired 
    private MockMvc mockMvc;

    @MockBean
    private AuthenticationManager authenticationManager;

    @Autowired
    private WebApplicationContext context;

    @Autowired
    private Filter springSecurityFilterChain;

    @Before
    public void setup() {
        mockMvc = MockMvcBuilders.webAppContextSetup(context)
                .addFilters(springSecurityFilterChain).build();
    }

    @Test
    public void testCreate() throws Exception {

        String exampleUserInfo = "{\"name\":\"Salam12333\",\"username\":\"[email protected]\",\"password\":\"Salam12345\"}";
        RequestBuilder requestBuilder = MockMvcRequestBuilders
                .post("/signup")
                .accept(MediaType.APPLICATION_JSON).content(exampleUserInfo)
                .contentType(MediaType.APPLICATION_JSON);

        MvcResult result = mockMvc.perform(requestBuilder).andReturn();

        MockHttpServletResponse response = result.getResponse();
        int status = response.getStatus();
        Assert.assertEquals("http response status is wrong", 200, status);
    }
}

In spring boot we do not require to add any thing additional for in memory database configuration except for jar file on class path and application property file (application.properties) on the class path (src/test/resources if maven is used) rest of the things will be taken care by spring boot (beauty of boot).

Another option is to provide profile specific properties file on the class path src/amin/resources (for example application-test.properties)

Both of the file are valid for test configurations

Sample configuration for property file is given below (consider HSQL DB jar on class path):

spring.jpa.hibernate.ddl-auto = create-drop
spring.jpa.database = HSQL
spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.HSQLDialect
spring.datasource.driverClassName = org.hsqldb.jdbcDriver
spring.datasource.url: jdbc:hsqldb:mem:scratchdb
spring.datasource.username = sa
spring.datasource.password = pass

Assuming you annotate class with @SpringBootApplication, which enables auto-configuration and you have H2 dependency on classpath(see below) Spring Boot will see H2 in-memory database dependency and it will create javax.sql.DataSource implementation. Default connection URL is jdbc:h2:mem:testdb and the default username and password are: username: sa and password: empty.

application.properties file

spring.datasource.url=jdbc:h2:mem:tesdb;DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=FALSE
    spring.datasource.driverClassName=org.h2.Driver
    spring.datasource.username=sa
    spring.datasource.password=

    spring.datasource.testWhileIdle = true
    spring.datasource.validationQuery = SELECT 1

    spring.jpa.show-sql = true
    spring.h2.console.enabled=true // if you need console

H2 Dependency

    <dependency>
      <groupId>com.h2database</groupId>
       <artifactId>h2</artifactId>
      <scope>runtime</scope>
   </dependency>

   <dependency> // If you need h2 web console 
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
   </dependency>

You can gain access to h2 console for management http://localhost:8080/h2-console