Mocked method inside lambda expression is not working

I am using the mockito but connection.prepareStatement is not getting matched and I am getting null as PreparedStatement. I have checked connection is getting mocked properly

void myMethod(){
    getJdbcTemplate().update(connection -> {
            PreparedStatement ps = connection.prepareStatement(addEmailData, new String[] { "mail_id" });
            ps.setString(++i, mailBean.getFromEmailId());

            return ps;
        }, keyHolder);
}

Below is the test case written

    void test(){
        when(connection.prepareStatement(anyString(),any(String[].class))).thenReturn(mock(PreparedStatement.class));
        when(dataSource.getConnection()).thenReturn(connection);
        myClass.init(dataSource);
        // Act
        myClass.myMethod(); 
    }

Can someone please advise how to return prepareStatement so that calls on PS can be tested

In fact, when testing the myMethod() method, you have to test the PreparedStatementCreator interface implementation, which is created by the connection -> { ... } lambda expression when calling the JdbcTemplate.update() method. To do this, you must capture the argument with which this method is called, so that you can then call it with a mock Connection implementation.

For example, you can do this.

Create mock implementations of the Connection, JdbcTemplate, and PreparedStatement interfaces.

Connection connection = Mockito.mock(Connection.class);
JdbcTemplate jdbcTemplate = Mockito.mock(JdbcTemplate.class);
PreparedStatement preparedStatement = Mockito.mock(PreparedStatement.class);

Create a captor for the PreparedStatementCreator implementation that is created in your method.

ArgumentCaptor<PreparedStatementCreator> preparedStatementCreatorCaptor = ArgumentCaptor.forClass(PreparedStatementCreator.class);

Define the behavior of a mock Connection implementation when the Connection.prepareStatement() method is called.

Mockito.when(connection.prepareStatement(Mockito.anyString(), Mockito.any(String[].class))).thenReturn(preparedStatement);

Execute your method with a mock JdbcTemplate implementation.

MyClass myClass = new MyClass(jdbcTemplate);
myClass.myMethod();

Make sure your method calls JdbcTemplate.update() and capture the PreparedStatementCreator implementation.

Mockito.verify(jdbcTemplate).update(preparedStatementCreatorCaptor.capture(), Mockito.any(KeyHolder.class));

Make sure that this PreparedStatementCreator implementation creates the exact PreparedStatement that your Connection returns.

Assertions.assertEquals(preparedStatement, preparedStatementCreatorCaptor.getValue().createPreparedStatement(connection));