Why is my mocked repository trying to connect to the database?

Question

So I'm trying to unittest the servicelayer of my "RESTful-like" API (RESTful-like because I'm not using Springboot or any other framework and instead try to code it from scratch...). The big problem here: the mocked repository, which I need for the service (-> cut), tries to connect to the database. The repository inherits from a HibernateController which of course has a SessionFactory and a Session for any connections but I thought, with mocking the object, I wouldn't have to worry about that and can just re-define the behaviour of its methods.

I tried using the @Mock annotation as well as the Mockito.mock() method.

Here are some samples of the repository, HibernateController and the test: Repository:

public class ArtikelRepository extends HibernateController implements Serializable {}

HibernateController:

public class HibernateController {
    private static SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
    private static Session session = sessionFactory.openSession();

public static void deleteById(Object id, Class deleteClass) {
        session.beginTransaction();
        session.delete(session.find(deleteClass, id));
        session.getTransaction().commit();
    }
...
}

Test:

@ExtendWith(MockitoExtension.class)
class ArtikelServiceUnittest {
    
    ArtikelRepository artikelRepository = Mockito.mock(ArtikelRepository.class);
    
    ArtikelService cut = new ArtikelService(artikelRepository);

    ArtikelEntity givenArtikelEntity = new ArtikelEntity(1, "Testartikel", "Test", 1, 1.00);

    @Test
    void shouldReturnAListWithTheGivenEntityAsDto() {
        // given
        List givenList = new ArrayList() {{
            add(givenArtikelEntity.toArtikelDto());
        }};
        when(artikelRepository.getAll("ArtikelEntity")).thenReturn(givenList);

        // when
        List result = cut.getAllArtikel();

        // then
        List expected = givenList;
        assertEquals(expected, result);
    }
}

And the error stacktrace:

Sep 29, 2022 2:32:32 PM org.hibernate.Version logVersion
INFO: HHH000412: Hibernate ORM core version 5.5.4.Final
Sep 29, 2022 2:32:32 PM org.hibernate.annotations.common.reflection.java.JavaReflectionManager <clinit>
INFO: HCANN000001: Hibernate Commons Annotations {5.1.2.Final}
Sep 29, 2022 2:32:32 PM org.hibernate.c3p0.internal.C3P0ConnectionProvider configure
INFO: HHH010002: C3P0 using driver: com.mysql.cj.jdbc.Driver at URL: jdbc:mysql://localhost:3306/cmp_sql
Sep 29, 2022 2:32:32 PM org.hibernate.c3p0.internal.C3P0ConnectionProvider configure
INFO: HHH10001001: Connection properties: {password=****, user=root}
Sep 29, 2022 2:32:32 PM org.hibernate.c3p0.internal.C3P0ConnectionProvider configure
INFO: HHH10001003: Autocommit mode: false
Sep 29, 2022 2:32:32 PM com.mchange.v2.log.MLog 
INFORMATION: MLog clients using java 1.4+ standard logging.
Sep 29, 2022 2:32:32 PM com.mchange.v2.c3p0.C3P0Registry 
INFORMATION: Initializing c3p0-0.9.5.5 [built 11-December-2019 22:18:33 -0800; debug? true; trace: 10]
Sep 29, 2022 2:32:32 PM org.hibernate.c3p0.internal.C3P0ConnectionProvider configure
INFO: HHH10001007: JDBC isolation level: <unknown>
Sep 29, 2022 2:32:32 PM com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource 
INFORMATION: Initializing c3p0 pool... com.mchange.v2.c3p0.PoolBackedDataSource@d3ec91c3 [ connectionPoolDataSource -> com.mchange.v2.c3p0.WrapperConnectionPoolDataSource@dbc22131 [ acquireIncrement -> 3, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, contextClassLoaderSource -> caller, debugUnreturnedConnectionStackTraces -> false, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, forceSynchronousCheckins -> false, identityToken -> 1hge2m2ar122sm961ef2fy9|61af1510, idleConnectionTestPeriod -> 0, initialPoolSize -> 3, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 0, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 15, maxStatements -> 0, maxStatementsPerConnection -> 0, minPoolSize -> 3, nestedDataSource -> com.mchange.v2.c3p0.DriverManagerDataSource@59aa486e [ description -> null, driverClass -> null, factoryClassLocation -> null, forceUseNamedDriverClass -> false, identityToken -> 1hge2m2ar122sm961ef2fy9|363a3d15, jdbcUrl -> jdbc:mysql://localhost:3306/cmp_sql, properties -> {password=******, user=******} ], preferredTestQuery -> null, privilegeSpawnedThreads -> false, propertyCycle -> 0, statementCacheNumDeferredCloseThreads -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, usesTraditionalReflectiveProxies -> false; userOverrides: {} ], dataSourceName -> null, extensions -> {}, factoryClassLocation -> null, identityToken -> 1hge2m2ar122sm961ef2fy9|45e1aa48, numHelperThreads -> 3 ]
Sep 29, 2022 2:33:03 PM com.mchange.v2.resourcepool.BasicResourcePool 
WARNUNG: com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@1a9d92ed -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: 
com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
    at com.mysql.cj.jdbc.exceptions.SQLError.createCommunicationsException(SQLError.java:174)
    at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:64)
    at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:828)
    at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:448)
    at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:241)
    at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:198)
    at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:175)
    at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:220)
    at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206)
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203)
    at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1176)
    at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1163)
    at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44)
    at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1908)
    at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)
Caused by: com.mysql.cj.exceptions.CJCommunicationsException: Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
    at java.base/jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandleAccessor.java:67)
    at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499)
    at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:483)
    at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:61)
    at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:105)
    at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:151)
    at com.mysql.cj.exceptions.ExceptionFactory.createCommunicationsException(ExceptionFactory.java:167)
    at com.mysql.cj.protocol.a.NativeSocketConnection.connect(NativeSocketConnection.java:89)
    at com.mysql.cj.NativeSession.connect(NativeSession.java:120)
    at com.mysql.cj.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:948)
    at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:818)
    ... 12 more
Caused by: java.net.ConnectException: Connection refused: connect
    at java.base/sun.nio.ch.Net.connect0(Native Method)
    at java.base/sun.nio.ch.Net.connect(Net.java:579)
    at java.base/sun.nio.ch.Net.connect(Net.java:568)
    at java.base/sun.nio.ch.NioSocketImpl.connect(NioSocketImpl.java:585)
    at java.base/java.net.SocksSocketImpl.connect(SocksSocketImpl.java:327)
    at java.base/java.net.Socket.connect(Socket.java:633)
    at com.mysql.cj.protocol.StandardSocketFactory.connect(StandardSocketFactory.java:153)
    at com.mysql.cj.protocol.a.NativeSocketConnection.connect(NativeSocketConnection.java:63)
    ... 15 more

Sep 29, 2022 2:33:03 PM com.mchange.v2.resourcepool.BasicResourcePool 
WARNUNG: com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask@44c22528 -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception: 
com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure

Process finished with exit code -1

Maybe any ideas what to do/what I'm missing or workarounds for the HibernateController-connection?

Answer 1

Its attempting to connect because sessionFactory and session are static and will be initialised when the class is loaded. To avoid this change them to instance variables

public class HibernateController {
    private final SessionFactory sessionFactory;
    private final Session session; 
    public HibernateController() {
        sessionFactory = HibernateUtil.getSessionFactory();
        session = sessionFactory.openSession();
    }