How to mock jdbc connection and resultSet using Mockito in TestNG

Question

I have to write some unit tests but I have problem with mocking ResultSet and jdbc Connection.

I have this method:

@Test
public void test3() throws SQLException, IOException {

    Connection jdbcConnection = Mockito.mock(Connection.class);
    ResultSet resultSet = Mockito.mock(ResultSet.class);

    Mockito.when(resultSet.next()).thenReturn(true).thenReturn(true).thenReturn(true).thenReturn(false);
    Mockito.when(resultSet.getString(1)).thenReturn("table_r3").thenReturn("table_r1").thenReturn("table_r2");
    Mockito.when(jdbcConnection
            .createStatement()
            .executeQuery("SELECT name FROM tables"))
            .thenReturn(resultSet);

    //when
    List<String> nameOfTablesList = null;
    try {
        nameOfTablesList = Helper.getTablesName(jdbcConnection);
    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    //then
    Assert.assertEquals(nameOfTablesList.size(), 3);
}

And error is showing in line executeQuery("SELECT name FROM tables") and it sounds like this:

java.lang.NullPointerException HelperTest.test3(HelperTest.java:71)

Any ideas whats going wrong?

Answer 1

You need to create an expectation on jdbcConnection.createStatement().

By default, I believe a null is returned.

Should read something like:

ResultSet resultSet = Mockito.mock(ResultSet.class);
Mockito.when(resultSet.next()).thenReturn(true).thenReturn(true).thenReturn(true).thenReturn(false);
Mockito.when(resultSet.getString(1)).thenReturn("table_r3").thenReturn("table_r1").thenReturn("table_r2");

Statement statement = Mockito.mock(Statement.class);
Mockito.when(statement.executeQuery("SELECT name FROM tables")).thenReturn(resultSet);

Connection jdbcConnection = Mockito.mock(Connection.class);
Mockito.when(jdbcConnection.createStatement()).thenReturn(statement);