spring unit test repository save not working - spring

Question

I'm trying to write a unit test, for my spring server.
First it will check if a username is present or not in repository, if not so the username is available, then it will return true, and then I will save that username to my repository and check if available ot not it should return false.
Here is my code:
#Test
public void availableTest() {
String username="some_username";
LoginCredential lc=new LoginCredential();
lc.setUsername(username);
lc.setPasswordHash("1");
lc.setSessionID(0);
assertEquals(true, loginCredentialService.available(username));
loginCredentialRepository.save(lc);
assertEquals(false, loginCredentialService.available(username));
}
But for some reason, for the last assertEquals it gives me error. So I can say, the data is not being saved in repository, as I have tested my APIs using postman.
So how this can be resolved?
I think testing class is properly annotated:
#RunWith(SpringRunner.class)
#SpringBootTest
public class MainApplicationTests {
#Autowired
private LoginCredentialService loginCredentialService;
#MockBean
private LoginCredentialRepository loginCredentialRepository;
...

Answer 1

You tagged the OP with H2, so I guess you know about In-Memory databases.
If you use the #SpringBootTest annotation, you are writing an integration test, so you'll test the full application as wired by Spring. For efficiency you might want to use an in-memory database for testing instead of a full SQL Server.
You can achieve this by adding H2 database as a test dependency, which will be picked up by Spring Boot for integration test repositories. Then you can inject the actual repository:
#Autowired
private LoginCredentialRepository loginCredentialRepository;
Additionaly, you can make your test #Transactional. Then every test case will run in a separate transaction, and the transaction will be rolled back after every test, so you don't need to worry about cross-test polution.
If you just want to Unit Test the LoginCredentialService, you need to stub the relevant methods on the repository, e.g.
#MockBean
private LoginCredentialRepository loginCredentialRepository;
#Test
public void availableTest1() {
when(loginCredentialRepository.existByName(username)).thenReturn(true);
assertEquals(false, loginCredentialService.available(username));
}
#Test
public void availableTest2() {
when(loginCredentialRepository.existByName(username)).thenReturn(false);
assertEquals(true, loginCredentialService.available(username));
}
You can do this as a pure Mockito test, too, without #SpringBootTest.