JUnit 5 Eclipse Java Testing

Question

I am doing JUnit5 testing using Mockito and here is the full code please have a look and let me know how to fix this :

package hotel.entities;

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

import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.junit.jupiter.api.function.Executable;

import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.Spy;
import org.mockito.junit.jupiter.MockitoExtension;

import hotel.credit.CreditCard;

import static org.mockito.Mockito.*;
import static org.mockito.ArgumentMatchers.any;
import static org.mockito.ArgumentMatchers.anyInt;

import java.util.ArrayList;
import java.util.Date;

class RoomTest {

    @Mock Booking booking;
    @Spy ArrayList <Booking> bookings;

    int roomID = 1;
    int stayLength = 1;
    RoomType roomtype = RoomType.SINGLE; 

    @InjectMocks Room room = new Room(roomID, roomtype);



    @BeforeEach
    void setUp() throws Exception {
        room = new Room(roomID,roomtype);
        //booking = new Booking(guest, room,bookedArrival,stayLength,numberOfOccupants,creditCard);
        //booking = new checkout(booking);
    }

    @AfterEach
    void tearDown() throws Exception {
    }

    @Test
    void roomCheckin() {
        room.checkin();
        assertTrue(room.isAvailable(null, stayLength));
        Executable e = () -> room.checkin();
        Throwable t = assertThrows(RuntimeException.class, e);
    }

    @Test
    void roomCheckout() {

        bookings.add(booking);
        room.checkin();
        assertEquals(roomID , bookings.size());
        assertTrue(room.isAvailable(null, stayLength));
        room.checkout(booking);

        verify(bookings).remove(booking);
        assertTrue(room.isReady());
        assertEquals(0,bookings.size());
    }

}

I am getting error on this line while I am doing testing: bookings.add(booking);

please tell me how can I fix this null pointer exception from the code so that it runs properly and my tests get successful.

Here is the complete error trace please guide me how to fix this issue:

java.lang.NullPointerException
    at hotel.entities.RoomTest.roomCheckout(RoomTest.java:60)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:436)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:115)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$6(TestMethodTestDescriptor.java:170)
    at org.junit.jupiter.engine.execution.ThrowableCollector.execute(ThrowableCollector.java:40)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:166)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:113)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:58)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.lambda$executeRecursively$3(HierarchicalTestExecutor.java:112)
    at org.junit.platform.engine.support.hierarchical.SingleTestExecutor.executeSafely(SingleTestExecutor.java:66)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.executeRecursively(HierarchicalTestExecutor.java:108)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.execute(HierarchicalTestExecutor.java:79)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.lambda$executeRecursively$2(HierarchicalTestExecutor.java:120)
    at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(Unknown Source)
    at java.util.stream.ReferencePipeline$2$1.accept(Unknown Source)
    at java.util.Iterator.forEachRemaining(Unknown Source)
    at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Unknown Source)
    at java.util.stream.AbstractPipeline.copyInto(Unknown Source)
    at java.util.stream.AbstractPipeline.wrapAndCopyInto(Unknown Source)
    at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(Unknown Source)
    at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(Unknown Source)
    at java.util.stream.AbstractPipeline.evaluate(Unknown Source)
    at java.util.stream.ReferencePipeline.forEach(Unknown Source)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.lambda$executeRecursively$3(HierarchicalTestExecutor.java:120)
    at org.junit.platform.engine.support.hierarchical.SingleTestExecutor.executeSafely(SingleTestExecutor.java:66)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.executeRecursively(HierarchicalTestExecutor.java:108)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.execute(HierarchicalTestExecutor.java:79)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.lambda$executeRecursively$2(HierarchicalTestExecutor.java:120)
    at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(Unknown Source)
    at java.util.stream.ReferencePipeline$2$1.accept(Unknown Source)
    at java.util.Iterator.forEachRemaining(Unknown Source)
    at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Unknown Source)
    at java.util.stream.AbstractPipeline.copyInto(Unknown Source)
    at java.util.stream.AbstractPipeline.wrapAndCopyInto(Unknown Source)
    at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(Unknown Source)
    at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(Unknown Source)
    at java.util.stream.AbstractPipeline.evaluate(Unknown Source)
    at java.util.stream.ReferencePipeline.forEach(Unknown Source)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.lambda$executeRecursively$3(HierarchicalTestExecutor.java:120)
    at org.junit.platform.engine.support.hierarchical.SingleTestExecutor.executeSafely(SingleTestExecutor.java:66)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.executeRecursively(HierarchicalTestExecutor.java:108)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor$NodeExecutor.execute(HierarchicalTestExecutor.java:79)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:55)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:43)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:170)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:154)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:90)
    at org.eclipse.jdt.internal.junit5.runner.JUnit5TestReference.run(JUnit5TestReference.java:89)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:41)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:541)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:763)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:463)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:209)

Answer 1

Based on your code snippet, it looks like you have two methods ie book the hotel and check-out the same. The general concept of unit test to test the code written in that particular class. So, your end goal will be to test book and checkout method in the different test case.

You are getting java.lang.NullPointerException because your bookings attribute is null due to wrong use of @Spy annotation.

@Spy 
List <Booking> bookings = new ArrayList<>();

You should use @Spy as shown above and it will solve your null pointer exception:

You can refer below link to read how to use @Spy @ https://www.baeldung.com/mockito-spy