calling method on object returned by when().thenReturn()

After doing lots of research, I didn't find the answer for this question in JUnits in java.

What I want to do is: To call some method on object returned by when().thenReturn(object) call.

e.g.:

<!-- language-all: lang-java -->

public boolean checkUpdate(String str, String endStr){
	GetEndpointRequest geaReq = new 
    GetEndpointRequest().withEndpointArn(endpointArn);
	GetEndpointResult geaRes = amazonSNS.getEndpointAttributes(geaReq);
	
	
	return !geaRes.getAttributes().get("Token").equals(token) || !geaRes.getAttributes().get("Enabled").equalsIgnoreCase("true");
}

And here is the Test method:

import com.amazonaws.services.sns.model.GetEndpointAttributesRequest;
import com.amazonaws.services.sns.model.GetEndpointAttributesResult;

@Tested
AmazonSNSRegistrationService service= new AmazonSNSRegistrationService();
service.amazonSNS = mock(AmazonSNS.class);

@Test
public void checkUpdateTest(){
    String pushToken = "dxbv1fwJYIo";
	String strToken = "";
    String strEnabled = "";
	String endPointArn = "";

	Map<String, String> jsonBody = new HashMap<String, String>();
	jsonBody.put("Token", "");
	jsonBody.put("enabled", "");

	
    GetEndpointAttributesRequest getEndpointReq =mock(GetEndpointAttributesRequest.class);		
	GetEndpointAttributesResult getEndpointRes =mock(GetEndpointAttributesResult.class);
	getEndpointRes.setAttributes(jsonBody);
	
	when(service.amazonSNS.getEndpointAttributes(getEndpointReq)).thenReturn(getEndpointRes);

	when(getEndpointRes.getAttributes()).thenReturn(jsonBody);
	when(getEndpointRes.getAttributes().get(strToken)).thenReturn("");
	when(getEndpointRes.getAttributes().get(strEnabled)).thenReturn("");
	amazonSNSRegistrationService.checkUpdate(pushToken, endPointArn);
}

I'm getting NullPointerException in checkUpdate() method on line -- "return !geaRes.getAttributes().get("Token").equals(token)".

As, geaRes is null.

How to solve this?

Adding another simple example , where I face this issue:

AmazonSNSRegistrationSerice.java:

public boolean deletePlatformApplicationArn(String deviceId, String appId){
	boolean isArnDeleted = false;
	try {
		DeleteEndpointRequest deleteEndpointReq = new DeleteEndpointRequest().withEndpointArn(appId);
		DeleteEndpointResult result = amazonSNS.deleteEndpoint(deleteEndpointReq);
		if (result.getSdkHttpMetadata().getHttpStatusCode() == HttpStatus.SC_OK) {
			AWSUtil.deleteArnEndpoint(deviceId, appId);
			isArnDeleted = true;
		}

	} catch (Exception e) {
	
		ErrorLogEventHelper.logErrorEvent(this.getClass().getName(), "Exception while deleting AWS ARN (endpoint)" + e.getMessage(), "deletePlatformApplicationArn", e, ErrorLogEvent.ERROR_SEVERITY);
	}
	return isArnDeleted;			
}

AmazonSNSRegistrationSericeTest.java:

@Test
public void deletePlatformApplicationArnTest(){
	String appId = "arn:aws:sns";
	String deviceId = "dev_1"; 
	DeleteEndpointRequest deleteEndpointReq = mock(DeleteEndpointRequest.class);
	DeleteEndpointResult result = mock(DeleteEndpointResult.class);
	

	when(amazonSNSRegistrationService.amazonSNS.deleteEndpoint(deleteEndpointReq)).thenReturn(result);
	
	SdkHttpMetadata metadata = mock(SdkHttpMetadata.class);
	when(result.getSdkHttpMetadata()).thenReturn(metadata);
	when(result.getSdkHttpMetadata().getHttpStatusCode()).thenReturn(HttpStatus.SC_OK);
	
	amazonSNSRegistrationService.deletePlatformApplicationArn(deviceId, appId);
}

Again the result object in if(result.getSdkHttpMetadata()) is coming NULL.

So first of all, you're trying to get an empty value out of your JsonMap:

@Test
public void checkUpdateTest(){
    String strToken = "";
.
.
.
    when(getEndpointRes.getAttributes().get(strToken)).thenReturn("");
    // so what you ask here is this:
    when(getEndpointRes.getAttributes().get("")).thenReturn("");
    // this should probably be "Token"
    when(getEndpointRes.getAttributes().get("Token")).thenReturn("");
}

the next thing is, the JsonMap is a real object and not a mock so you don't need to call when(getEndpointRes.getAttributes().get(strToken)).thenReturn(""); as your jsonmap is going to return the right value.

then, this call is not needed as your getEndpointRes is a mock. That's why you use the when().thenX() syntax

    getEndpointRes.setAttributes(jsonBody);

To resolve your NPE problem try the following:

// imports...

@Tested
AmazonSNSRegistrationService service= new AmazonSNSRegistrationService();

@Test
public void checkUpdateTest(){
    // directly mock the amazonsns here
    AmazonSNS amazonSNS = mock(AmazonSNS.class);
    service.amazonSNS = amazonSNS;

    String pushToken = "dxbv1fwJYIo";
    String endPointArn = "";

    // maybe mock them aswell
    Map<String, String> jsonBody = new HashMap<String, String>();
    jsonBody.put("Token", "");
    jsonBody.put("enabled", "");


    // deleted the mocked request. You don't need it in this case as your service contructs it by itself     
    GetEndpointAttributesResultgetEndpointRes getEndpointRes = mock(GetEndpointAttributesResult.class);
    getEndpointRes.setAttributes(jsonBody);

    // directly use the mocked object and react on any() as getEntpointReq never will be present in your service!
    when(amazonSNS.getEndpointAttributes(any())).thenReturn(getEndpointRes);

    when(getEndpointRes.getAttributes()).thenReturn(jsonBody);
    amazonSNSRegistrationService.checkUpdate(pushToken, endPointArn);
    // do some further assertments
}

It seems that you try to mock things that you don't need to mock and mock things that are generated in your service. If you ever encounter a NPE in the classes you are trying to test you should debug your test properly. In your case the mocking seems incorrect and therefore the real object calls result in NPEs

In your second example it seems to be the same issue. you try to return something from an mock, that is probably created inside your amazonSNSRegistrationService. How should your mocked deleteEndpointReq return any value if it is not part of the class? You simple create the mock, but it is not the same object that is created inside of you service!

And after all you should add some assertions. The tests I see here only fail if the tested class fails with an error like in your case. But some basic assertions are missing. I personally use the AAA pattern for unit tests.