JUnit5 SpringBootTest NullPointerException when testing Service - junit5

Question

I am following a tutorial for unit testing a Service, and I am attempting to use JUnit5 instead of JUnit4 (which is what the tutorial uses). The test works fine when I follow the tutorial exactly with JUnit4, but I get a NullPointerException with JUnit5.
The repository:
public interface CourseRepo extends CrudRepository<Course, Long> {}
The service:
#Service
public class CourseService {
private final CourseRepo courseRepo;
public CourseService(CourseRepo courseRepo) {
this.courseRepo = courseRepo;
}
public Course save(Course course) {
Course newCourse = courseRepo.save(course);
return newCourse;
}
}
The test:
package com.elovell.blackboard.service;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.mockito.ArgumentMatchers.any;
import static org.mockito.Mockito.when;
import com.elovell.blackboard.domain.Course;
import com.elovell.blackboard.repository.CourseRepo;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.MockitoAnnotations;
import org.mockito.junit.jupiter.MockitoExtension;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
#ExtendWith(MockitoExtension.class)
#SpringBootTest(webEnvironment = WebEnvironment.NONE)
public class CourseServiceTest {
#Mock
public CourseRepo courseRepo;
#InjectMocks
public CourseService courseService;
#BeforeEach
public void setUp() {
MockitoAnnotations.initMocks(this);
}
#Test
public void testSaveCourse() {
Course mockCourse = new Course();
mockCourse.setPk1(1L);
mockCourse.setCourseId("ENGL101");
when(courseRepo.save(any(Course.class))).thenReturn(mockCourse);
// save(null) should still return mockCourse
Course newCourse = courseService.save(null);
assertEquals("ENGL101", newCourse.getCourseId());
}
}
Here is the first few lines of the Exception:
java.lang.NullPointerException
at com.elovell.blackboard.service.CourseServiceTest.testSaveCourse(CourseServiceTest.java:44)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
The test and dependencies portion of my build file:
test {
useJUnitPlatform {
includeEngines 'junit-jupiter'
}
}
dependencies {
implementation 'org.springframework.boot:spring-boot-starter-data-jpa'
implementation 'org.springframework.boot:spring-boot-starter-web'
runtimeOnly 'com.h2database:h2'
testImplementation 'org.springframework.boot:spring-boot-starter-test'
testImplementation("org.junit.jupiter:junit-jupiter-api:5.5.1")
testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:5.1.0")
testCompile 'org.mockito:mockito-junit-jupiter:2.23.4'
}

Answer 1

This looks like you trying to mix an integration test with unit tests.
When you use the #SpringBootTest annotation then SpringExtension for Junit5 starts an application context before running your test, and to make mocks in tests you need to use #MockBean annotation instead of #Mock & #InjectMocks. This is a different scope of tests.
As I see, you need just a unit test and you can remove the SpringBootTest annotation.
By the way, I think you got NPE because of you any(Course.class) in when(courseRepo....
Try to use isNull() or any() (without specification concrete class).