[FIXED] Junit5 returning Map from @MethodSource annotation

Issue

I'm using @MethodSource annotation on my Junit test case in order to receive from another method a Map<String, Object>.

Seems that @MethodSource cannot support "Map" object.

This is the error I received: org.junit.platform.commons.PreconditionViolationException: Cannot convert instance of java.util.HashMap into a Stream: {1=Obj1, 2=Obj2}

Do you know if there is a way to receive back a "Map" object like in this example?

@ParameterizedTest
@MethodSource("hashMapProvider")
void testMyMapObj(Map<String, Object> argument) {
    assertNotNull(argument);
    Object obj1 = argument.get("1");
}


static Map<String, Object> hashMapProvider() {
    Map<String, Object> map = new HashMap<>();
    map.put("1", "Obj1");
    map.put("2", "Obj2");
    return map;
 }

Solution

If your argument in test method is Map<String, Object>, use as return value Stream<Map<String, Object>> in source method:

import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.MethodSource;

import java.util.Map;
import java.util.stream.Stream;

import static org.junit.jupiter.api.Assertions.assertNotNull;

class SimpleTest {

    @ParameterizedTest
    @MethodSource("hashMapProvider")
    void test(Map<String, Object> argument) {
        System.out.println(argument);
        assertNotNull(argument);
    }

    static Stream<Map<String, Object>> hashMapProvider() {
        return Stream.of(
                Map.of("1", "Obj1", "2", "Obj2"),
                Map.of("3", "Obj3")
        );
    }
}

Answered By - Georgy Lvov
Answer Checked By - Dawn Plyler (JavaFixing Volunteer)