Multi-Answer Mockito

ArrayMatcherAnswer.java

import java.util.LinkedList;
import java.util.List;

import org.mockito.ArgumentMatcher;
import org.mockito.invocation.InvocationOnMock;
import org.mockito.stubbing.Answer;

import lombok.AllArgsConstructor;
import lombok.Setter;
import lombok.experimental.Accessors;

/**
 * Helpers class to match multi calls to the same method.
 * @param <T> Argument type.
 * @param <R> Result type.
 */
@Accessors(fluent = true)
public class ArrayMatcherAnswer<T, R> implements Answer<R>, ArgumentMatcher<T> {

    @AllArgsConstructor
    private static class AnswerMock<T, R> {

        private final ArgumentMatcher<T> matcher;

        private final R result;
    }

    private final List<AnswerMock<T, R>> array = new LinkedList<>();

    @Setter
    private R defaultResult;

    private AnswerMock<T, R> currentMock;

    /**
     * Add an argument matcher with the attached result.
     * @param matcher Argument matcher.
     * @param result Result to return.
     * @return this
     */
    public ArrayMatcherAnswer<T, R> add(final ArgumentMatcher<T> matcher, final R result) {
        this.array.add(new AnswerMock<>(matcher, result));
        return this;
    }

    /**
     * Add an argument matcher with the default result.
     * @param matcher Argument matcher.
     * @return this
     */
    public ArrayMatcherAnswer<T, R> add(final ArgumentMatcher<T> matcher) {
        return this.add(matcher, this.defaultResult);
    }

    /**
     * Add an argument with the default result.
     * Use {@linkplain Object#equals(Object)} as {@linkplain ArgumentMatcher}.
     * @param object Argument
     * @return this
     */
    public ArrayMatcherAnswer<T, R> add(final T object) {
        return this.add(object, this.defaultResult);
    }

    /**
     * Add an argument with the given result.
     * Use {@linkplain Object#equals(Object)} as {@linkplain ArgumentMatcher}.
     * @param object Argument
     * @param result Result to return.
     * @return this.
     */
    public ArrayMatcherAnswer<T, R> add(final T object, final R result) {
        return this.add(object::equals, result);
    }

    @Override
    public R answer(final InvocationOnMock invocation) throws Throwable {
        return this.currentMock.result;
    }

    @Override
    public boolean matches(final T argument) {
        this.currentMock = this.array.stream()
                        .filter(a -> a.matcher.matches(argument))
                        .findAny()
                        .orElse(null);
        return this.currentMock != null && this.array.remove(this.currentMock);
    }

}

ArrayMatcherAnswer.md

ArrayMatcherAnswer

Simple example:

final var expected = List.of("yes", "no");
final var matchers = new ArrayMatcherAnswer<Integer, String>()
                        .defaultResult("yes")
                        .add(1)
                        .add(2, "no");
Mockito.when(this.subService.jane(ArgumentMatchers.argThat(matchers))))
    .thenAnswer(matchers);
final var results = this.service.doe();
Assertions.assertEquals(expected, results);