[FIXED] Test login Servlet

Issue

I tried to test my login servlet using mockito, but it return the error:

java.lang.NullPointerException: Cannot invoke "java.io.PrintWriter.println(String)" because "out" is null. at control.LoginPatient.doPost(LoginPatient.java:55) at control.LoginPatientTest.testDoPostSuccessfull(LoginPatientTest.java:64)

Here the code of my Login servlet:

package control;

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import model.ProfileManager;
import model.Bean.UserBean;

/**
 * Servlet implementation class LoginPatient
 */
@WebServlet("/LoginPatient")
public class LoginPatient extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public LoginPatient() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String fiscal_code=request.getParameter("fiscal_code");
        String user_password= request.getParameter("user_password");
        PrintWriter out = response.getWriter();
        ProfileManager pM=new ProfileManager();
        UserBean patient= pM.ReturnPatientByKey(fiscal_code, user_password);

        if(patient != null) {
            HttpSession session= request.getSession();
            session.setAttribute( "user" , patient);
            session.setMaxInactiveInterval(-1);
            out.println("1");
        }

        else {
            out.println("0"); 
        }
    }

}

and here my test case:

class LoginPatientTest {

    private LoginPatient loginPatient;
    private HttpServletRequest mockedRequest;
    private HttpServletResponse mockedResponse;
    private ServletContext mockedServletContext;
    private HttpSession mockedSession;
    private PatientBean patient;
    private ProfileManager pm;
    private PrintWriter mockedOut;
    
    /**
     * @throws java.lang.Exception
     */
    @BeforeEach
    void setUp() throws Exception {
        loginPatient = new LoginPatient();
        mockedRequest = Mockito.mock(HttpServletRequest.class);
        mockedResponse = Mockito.mock(HttpServletResponse.class);
        mockedSession = Mockito.mock(HttpSession.class);
        mockedServletContext = Mockito.mock(ServletContext.class);
        mockedOut = Mockito.mock(PrintWriter.class);
        patient = Mockito.mock(PatientBean.class);
        pm = Mockito.mock(ProfileManager.class);
    }

    /**
     * @throws java.lang.Exception
     */
    @AfterEach
    void tearDown() throws Exception {
    }

    /**
     * Test method for {@link control.LoginPatient#doPost(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)}.
     * @throws javax.servlet.ServletException
     * @throws java.io.IOException
     */ 
    @Test
    final void testDoPostSuccessful() throws ServletException, IOException{
        
Mockito.doReturn(mockedServletContext).when(mockedRequest).getServletContext();
        Mockito.when(mockedRequest.getParameter("fiscal_code")).thenReturn("fiscalCode");
        Mockito.when(mockedRequest.getParameter("user_password")).thenReturn("password");
        Mockito.when(mockedRequest.getSession()).thenReturn(mockedSession);
        Mockito.when(pm.ReturnPatientByKey("fiscalCode", "password"));
        Mockito.when(mockedResponse.getWriter()).thenReturn(mockedOut);

loginPatient.doPost(mockedRequest, mockedResponse);

        Mockito.verify(mockedOut).println("1");
        Mockito.verify(mockedSession).setAttribute(Mockito.eq("user"), patient);
    }

}

I don't use Spring

Update: Now it gives me another error:

org.mockito.exceptions.misusing.InvalidUseOfMatchersException: Invalid use of argument matchers! 2 matchers expected, 1 recorded: -> at control.LoginPatientTest.testDoPostSuccessful(LoginPatientTest.java:75) This exception may occur if matchers are combined with raw values: //incorrect: someMethod(anyObject(), "raw String"); When using matchers, all arguments have to be provided by matchers. For example: //correct: someMethod(anyObject(), eq("String by matcher")); For more info see javadoc for Matchers class. at control.LoginPatientTest.testDoPostSuccessful(LoginPatientTest.java:75) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:64) at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.base/java.lang.reflect.Method.invoke(Method.java:564) at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:686) at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60) at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131) at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:149) at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:140) at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:84) at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115) at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105) at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106) at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64) at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45) at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37) at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104) at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$6(TestMethodTestDescriptor.java:205) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:201) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:137) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:71) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:135) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125) at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80) at java.base/java.util.ArrayList.forEach(ArrayList.java:1511) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125) at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80) at java.base/java.util.ArrayList.forEach(ArrayList.java:1511) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125) at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32) at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57) at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:248) at org.junit.platform.launcher.core.DefaultLauncher.lambda$execute$5(DefaultLauncher.java:211) at org.junit.platform.launcher.core.DefaultLauncher.withInterceptedStreams(DefaultLauncher.java:226) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:199) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:141) at org.eclipse.jdt.internal.junit5.runner.JUnit5TestReference.run(JUnit5TestReference.java:98) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:41) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:542) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:770) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:464) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:210)

Solution

Issue 1:

In the mock setup change mockedOut variable to mockedOut = Mockito.mock(PrintWriter.class);

Issue 2:

You mocked out mockedOut variable after you fires the business logic. You should change the order. Mock everything before the business logic is invoked.

//Given

    Mockito.doReturn(mockedServletContext).when(mockedRequest).getServletContext();
    Mockito.when(mockedRequest.getParameter("fiscal_code")).thenReturn("fiscalCode");
    Mockito.when(mockedRequest.getParameter("user_password")).thenReturn("password");
    Mockito.when(mockedRequest.getSession()).thenReturn(mockedSession);
    Mockito.when(pm.ReturnPatientByKey("fiscalCode", "password"));
    Mockito.when(mockedResponse.getWriter()).thenReturn(mockedOut);

//When   
    loginPatient.doPost(mockedRequest, mockedResponse);   


//Then
    Mockito.verify(mockedOut).println("1");
    Mockito.verify(mockedSession).setAttribute(Mockito.eq("user"), patient);

Answered By - tomeszmh