Junit Test case Initialize a class getting Error

Question

I am writing a Junit test case for StandardAlone java class. I am getting nullPointerException while initialize the Class object. here is my code. Any help much appreciated

Here is my class

@RunWith(MockitoJUnitRunner.class)
public class ABCGeneratorApplicationTest extends TestCase {

   // @Autowired
    MyFileReader myFileReader;

public ABCGeneratorApplicationTest (MyFileReader myFileReader) {

    this.myFileReader= myFileReader;
}

@Before
public void setUp() throws Exception {


}

@Test
public void instrumentRead()
{
    String[] args = {"20180518","0002"};
    Stream<Employee> empList= myFileReader.read(args);
    Assert.assertNotNull(instrumentStream);
}

Implementation class

public class MyFileReader {

public Stream<Employee> read(String[] runArguments){

    try {
        Path path = getFilePath(runArguments);

        return Files.lines(path,getEncoding()).skip(1)
                .map(this::parseRow)
                .filter(this::filterRow);

    } catch (IOException e) {
        return Stream.empty();
    }catch(Exception e) {
        e.printStackTrace();
        return Stream.empty();
    }

}

Here is the error I am getting :

java.lang.Exception: Test class should have exactly one public zero-argument constructor

at org.junit.runners.BlockJUnit4ClassRunner.validateZeroArgConstructor(BlockJUnit4ClassRunner.java:171) at org.junit.runners.BlockJUnit4ClassRunner.validateConstructor(BlockJUnit4ClassRunner.java:148) at org.junit.runners.BlockJUnit4ClassRunner.collectInitializationErrors(BlockJUnit4ClassRunner.java:127) at org.junit.runners.ParentRunner.validate(ParentRunner.java:416) at org.junit.runners.ParentRunner.(ParentRunner.java:84) at org.junit.runners.BlockJUnit4ClassRunner.(BlockJUnit4ClassRunner.java:65) at org.mockito.internal.runners.DefaultInternalRunner$1.(DefaultInternalRunner.java:27) at org.mockito.internal.runners.DefaultInternalRunner.(DefaultInternalRunner.java:27) at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:423) at org.mockito.internal.runners.util.RunnerProvider.newInstance(RunnerProvider.java:27) at org.mockito.internal.runners.RunnerFactory.create(RunnerFactory.java:69) at org.mockito.internal.runners.RunnerFactory.createStrict(RunnerFactory.java:40) at org.mockito.junit.MockitoJUnitRunner.(MockitoJUnitRunner.java:152) at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:423) at org.junit.internal.builders.AnnotatedBuilder.buildRunner(AnnotatedBuilder.java:104) at org.junit.internal.builders.AnnotatedBuilder.runnerForClass(AnnotatedBuilder.java:86) at org.junit.runners.model.RunnerBuilder.safeRunnerForClass(RunnerBuilder.java:59) at org.junit.internal.builders.AllDefaultPossibilitiesBuilder.runnerForClass(AllDefaultPossibilitiesBuilder.java:26) at org.junit.runners.model.RunnerBuilder.safeRunnerForClass(RunnerBuilder.java:59) at org.junit.internal.requests.ClassRequest.getRunner(ClassRequest.java:33) at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:49) at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47) at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242) at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

The only thing that makes this question interesting is that the classloader is a bit special because of how Junit and Mockito does its thing. A stacktrace is an interesting piece of useful information. Otherwise, this is a duplicate of the many "how to solve NPEs" questions on this site. — user1531971

codeLover codeLover · Accepted Answer · 2018-07-17T04:49:39

It is because your test class(in this case ABCGeneratorApplicationTest) is not having any default public constructor(since you have only parametrized constructor). Just add a default public constructor, this exception would be resolved..

Junit Test case Initialize a class getting Error

1 Answers