[Java] Pass arguments to constructor in Mockito / Set method default call to callRealMethod

A little note from Mockito

Pass arguments to the constructor

package jp.jig.product.live.server.common.service;

import org.junit.Test;

import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.when;

public class ApiServiceTest {

    public static class ApiService {

        private final String endpoint;
        private final int timeout;

        public ApiService(String endpoint, int timeout) {
            this.endpoint = endpoint;
            this.timeout = timeout;

        public String request() {
            if (endpoint == null) {
                throw new IllegalStateException("endpoint is null");

            return endpoint;

        public boolean validTimeout() {
            return timeout > 0;

    public void test() {

        ApiService apiService = mock(ApiService.class);
        apiService.request(); // -> throw IllegalStateException


For example, when creating a mock of  ĽApiServiceas shown above and calling therequest ()` method. I think there are situations where you want to set a value in the constructor.

At this time, you can pass the argument to the constructor while creating a mock object by using MockSetting # useConstructor as the second argument ofmock ().

    public void test() {
        ApiService apiService = mock(ApiService.class, withSettings().useConstructor("http://localhost", 100));
        apiService.request(); // -> http://localhost

If you try to put logging in the constructor, the log will also be output, so you can see that the processing in the constructor is also being executed.

Make the default call callRealMethod

I basically want to call the original method when testing, but I want to mock only some of the methods. .. .. I think there is something like that.

ApiService apiService = mock(ApiService.class,

This defaults to callRealMethod by passing CALLS_REAL_METHODS to MockSetting # defaultAnswer.

However, there is one caveat, you need to be careful when using when () in a method that is callRealMethod.

    public void test() {
        ApiService apiService = mock(ApiService.class, withSettings().defaultAnswer(CALLS_REAL_METHODS));
        when(apiService.request()).thenReturn("hogehoge"); // -> throw IllegalStateException

The above code seems to work normally, but the method is called at the time of when (apiService.request ()). It seems better to use doReturn to avoid this.

    public void test() {
        ApiService apiService = mock(ApiService.class, withSettings().defaultAnswer(CALLS_REAL_METHODS));

        apiService.request(); // -> hogehoge

You can use doReturn to set the mock without calling callRealMethod.

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