Category Archives: Technology

A dive into Mockito – 3

Part 3 - Partial Mocks using Mockito and Limitations of Mockito

  • Partial Mocks – with mocks and spies
  • Create a mock of the class
  • Spy the class
  • Which method to use – mock or spy?
  • Limitations of Mockito

Full Series

Partial Mocks – with mocks and spies

Partial mocks are created when only some methods of a class need to be stubbed, and the real methods must be called for others.

Partial mocks can be created in two ways:

  1. Create a mock of the class
    This would create mock implementation of all the methods. For calling the real method, we must use thenCallRealMethod()
  2. Spy the class
    This is the opposite of creating mocks. This will call real methods, unless otherwise specified by stubs.

Let us consider having a method: String getEmail(String name)

Create a mock of the class

Partial mocks can be created in the following manner by creating mocks:

EmailManager managerMock = Mockito.mock(EmailManager.class);

This will call the real implementation of getEmail() method in the EmailManager. The mock implementations will be called for all other methods.

Spy the class

This is the method to create spies of real objects:

EmailManager manager = new EmailManager();
EmailManager managerSpy = Mockito.spy(manager);

This will call the stubbed implementation of getEmail() method in the EmailManager. The real implementation will be called for all other methods

Exception when spying:

While spying, remember that the actual methods are called. This can cause a lot of side effects, and sometimes Exceptions.

The primary reason for this is that the method call inside when() actually gets executed. So, even if the method is stubbed, it can internally call another method of the class which might not be stubbed, and the real method will be called.

The below code would fail:

List list = new LinkedList();
List spy = Mockito.spy(list);

A closer look at the stacktrace shows something like this:

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
  at java.util.LinkedList.entry(
  at java.util.LinkedList.get(

The get(0) internally calls entry() method(), which is not stubbed, causing the real method to be called.

To prevent this error, an alternative syntax must be used:


Which method to use – mock or spy?

To decide which method to use, take a look at how many methods need to be stubbed.

  • If more real methods need to be called, then use spy.
  • Otherwise, use mock

New, well-designed and test-driven code should not use partial mocks. Using partial mocks means that the actual code is badly designed. But that should not stop us from writing unit tests.

A bad unit test is better than no unit test.

Limitations of Mockito

Mockito has a few limitations

  • Cannot mock final classes
  • Cannot mock static methods
  • Cannot mock final methods – their real behaviour is executed without any exception. Mockito cannot warn you about mocking final methods, so be vigilant.
  • Cannot mock equals(), hashCode()

Future articles in the series:

  • Part 4 – Some complex examples and common mistakes in using Mockito

A dive into Mockito – 2

Part 2 – Argument Matchers and Stubbing Void Methods

  • Using Argument Matchers
  • A simple use of any() matcher
  • Writing Custom Argument Matchers
  • Stubbing void methods

Full Series

Using Argument Matchers

Mockito argument matchers can be used to specify the method arguments for stubbing. If the method has arguments but you really don’t care what gets passed or cannot predict it, argument matchers can be used.

Argument Matchers provide us a lot of flexibility in stubbing.

Argument Matchers use the equals() method for comparisons.

A simple use of any() matcher

Let us assume we have an EmailService that is trying to save an email ID using an EmailManager. This means that the save() method of the EmailService calls the save() method of the EmailManager, which in turn saves the email to the database. A simple unit test for the save() method of the EmailService can test whether the save() on the Manager was called.

import org.junit.Test;
import org.mockito.Mockito;

public class EmailServiceTest {
	public void testSaveEmail() {
		EmailManager manager = Mockito.mock(EmailManager.class);
		EmailService service = new EmailService(manager);"");


Note the use of the argument matcher in line 12:


We used the matcher because, we really do not care what parameter was passed on the save().

The generic any() matcher:

Mockito provides a matcher that matches any Object. Some valid variants of the above are:


The cast from Object to String is required in the first line, the lack of which will cause compilation error.

The second line shown above is most useful when we need to match custom classes we create in our application.
Assuming save() method saves a Person object, we would write:


While using argument matchers in stubbing, all arguments of a method must be matchers.

If our save method also takes in an integer, this line would throw error:

Mockito.verify(manager).save(12, Mockito.any(Person.class));

To fix the above scenario, we can write:

Mockito.verify(manager).save(Mockito.eq(12), Mockito.any(Person.class));

Some common Argument Matchers

any() or any(Class clazz)Any object (or object of a given class) or null

Any object of given type or null
eqDefault Matcher. Compares using equals() method
sameObject argument that is the same as the given value. Compares using ==
refEqObject argument that is reflection-equal to the given value. This Matcher can be used when equals() is not implemented on compared objects. Matcher uses Java reflection API to compare fields of wanted and actual objects.
Argument is null/not null
contains(String substring)
matches(String regex)
endsWith(String suffix)
startsWith(String prefix)
String-specific argument matchers

Writing Custom Argument Matchers

Consider this scenario. We have the following classes:

  • Person – A class with two variables – name, email id
  • PersonService – A service class that creates a Person object and calls savePerson() method on the manager
  • PersonManager – The manager class that needs to be mocked

We need to write test case for personLogic() method in PersonService

public class PersonService {
	private final PersonManager manager;

	public PersonService(PersonManager manager) {
		this.manager = manager;

	public void personLogic() {
		Person person = new Person("Karthik", "");

The below test will fail:

import org.junit.Test;
import org.mockito.Mockito;

public class PersonServiceTest {
	public void testPersonLogic() {
		PersonManager manager = Mockito.mock(PersonManager.class);
		PersonService service = new PersonService(manager);


		Person verifyPerson = new Person("Karthik", "");

Reason: The expected object, with reference verifyPerson is entirely different from the actual object, and the default equals() comparison which argument matchers use, fails.

Use Custom Argument Matcher

In this scenario, using custom argument matchers come in handy.

Lines 12 and 13 above can be replaced with this:

				Mockito.argThat(new ArgumentMatcher() {

					public boolean matches(Object argument) {
						Person person = (Person) argument;
						return person.getName().equals("Karthik")
								&& person.getEmail().equals("") ? true
								: false;

Alternate Solution – 1

Use the refEq matcher to compare the fields of the objects in hand:

Person verifyPerson = new Person("Karthik", "");

Alternate Solution – 2

Override the equals() method in Person class to compare objects.

Stubbing void methods

We face a lot of scenarios in our applications where we need to stub void methods. With void methods, stubbing is slightly different. We cannot use void methods in the when() call.

The alternative syntax is:


We can also test exception handling. How would my code handle if an exception is thrown by void methods

Mockito.doThrow(new RuntimeException()).when(mock).setAttribute(Mockito.anyString());

We can also set the behaviour of a void method to do nothing when called. This is not possible for non-void methods:


Why when() does not work for void methods:

Take a look at the syntax of when():


Notice that the method is called inside brackets. Compiler does not like void method inside brackets!!

The two ‘when()’ are different syntax.

Notice that the when() for a non-void method stubbing takes in a methodCall as parameter, whereas the when() in void method stubbing takes in a mock object.

doPrimarily used for stubbing void methods
doThrow(Throwable... throwables).when(mock).method();
doReturn(T value).when(mock).method();
doAnswer(Answer answer).when(mock).method();

Future articles in the series:

  • Part 3 – Partial Mocks using Mockito and Limitations of Mockito
  • Part 4 – Some complex examples and common mistakes in using Mockito

A dive into Mockito – 1

Part 1 – Getting Started with Mockito

  • Mocking Frameworks – Mockito
  • A simple use of Mockito
  • Verifying Interactions with the mock
  • Stubbing methods using when()

Full Series

Mocking Frameworks

Mocking Frameworks allow us to test the code you want, without its dependencies. In a unit test, mock objects can simulate the behaviour of complex objects that are impractical or impossible to incorporate into a unit test.

Mock objects isolate the unit of code you are testing.


This is a framework used for test stubbing and interaction testing.

Let us assume that we have a simple servlet, and a method testCheckFormat() that checks the format of the email id submitted in the HTML form. It is impractical to create an actual HttpServletRequest object for unit test. So we mock this object, in order to test the code we are interested in.

A simple use of Mockito

import javax.servlet.http.HttpServletRequest;
import org.junit.Assert;
import org.junit.Test;
import org.mockito.Mockito;

public class ServletFacadeTest {

	public void testCheckFormat() {
		HttpServletRequest requestMock = Mockito.mock(HttpServletRequest.class);

		ServletFacade servletFacade = new ServletFacade();
		boolean result = servletFacade.checkFormat(requestMock);

		Assert.assertEquals(true, result);

There are three fundamental steps in writing JUnit test cases with Mockito:

  1. Create a mock of the object on which the method under test is dependent [line 10]
  2. Specify behaviors on the mock object (stub) [line 11]
  3. Assert/verify test scenario [lines 14-16]

Verifying Interactions with the mock

One of the most important capabilities of Mockito is to verify whether the mock had any interactions. A mock object will remember all its invocations.

The following test would have passed in the above case:


It is also easy to ensure that there were no more interactions with our mock apart from getting the email:


Let’s assume that our logic now tries retrieving two details from the request, namely email and name. To test two invocations, we now can use:


We can write this slightly differently, using argument matchers provided by Mockito:

Mockito.verify(requestMock, Mockito.times(2)).getAttribute(Mockito.anyString());

Verifying a stubbed invocation is unnecessary and often leads to just redundant tests!

verify( T mock).someMethod();
verify( T mock, times(int n) ).someMethod();
verify( T mock, atLeast(int n) ).someMethod();
verify( T mock, atLeastOnce() ).someMethod();
verify( T mock, atMost(int n) ).someMethod();
verify( T mock, never() ).someMethod();
Verify that someMethod was called specified number of times. Default is once.
verifyZeroInteractions( Object... mocks );Verify that there have been no method calls on the mock object(s)
verifyNoMoreInteractions( Object... mocks )Verify that there have been no additional method calls on the mock object(s) besides what has already been verified.

Stubbing methods using when()

Stubbing is used to specify method behaviors on mock objects.
We have already seen an example of stubbing:


Argument matchers can be used in stubs to match the invocation with any specified argument:
In the below example, any invocation of getAttribute() with a String parameter will return the string “”.


Sometimes, we might have to test exception handling. How would my code handle if an exception is thrown by getAttribute()

Mockito.when(requestMock.getAttribute(Mockito.anyString())).thenThrow(new RuntimeException());

when() would work only for non-void methods!

whenOnly for non-void methods
when( mock.method() ).thenCallRealMethod();
when( mock.method() ).thenReturn(T value);
when( mock.method() ).thenReturn(T value, T... values);
when( mock.method() ).thenThrow(Throwable... throwables);
when( mock.method() ).thenAnswer(Answer answer);

This should get you started with some basic unit tests with Mockito. Have fun !! :)

Future articles in the series:

  • Part 2 – Argument Matchers and stubbing void methods
  • Part 3 – Partial Mocks using Mockito and Limitations of Mockito
  • Part 4 – Some complex examples and common mistakes in using Mockito

Natural Language Processing – Basics

Natural Language Processing

  • Making computers understand and deal with natural (human) languages like English, Tamil, Spanish, etc.
  • Exploiting human cleverness, and not computer cleverness

Natural Language Processing is a field of Computer Science and Linguistics concerned with the interactions between computers and natural (human) languages.


Phonology study of speech sounds
Morphology study of meaningful components of words
Syntax study of structural relationships between words
Semantics study of meaning


  • Modeling the pronunciation of a word as a string of symbols – PHONES
  • Involves study of syllables, how they sound and how they group together to produce the word sound.
  • Notice the difference in sound of “C” in the following words:
    • Coach
    • Chair
    • Can


  • Identification, analysis and description of the structure of words.
  • Study of structural variations of words
  • INFLECTIONS in a word are structural changes, usually through affixes, to express Number, Tense, Case, Gender, Person, etc.
    • dog – dogs
    • goose – geese
    • hunt – hunted
    • his – hers
  • WORD FORMATIONS includes a group of words that have a specific meaning when they appear together.
    • mother in law
    • hot dog


  • Study of grammars
  • Syntactic correctness in sentence formation
  • Part of Speech tagging
    • Noun
    • Verb
    • Adjective, etc
  • I can write : Is “can” AUX VERB or VERB or NOUN?


  • Understanding and representing the meaning

    A simple semantic network
  • Predicate Calculus can be used to represent semantics: Has(Ram, book)

Browse through the below presentation for more information on

  • NLP
  • Ambiguity resolution
  • Perceptions
  • Applications of NLP
  • Machine Learning

Java Java jing-jing-jing … !

This song makes me love Java even more I normally do !!!

Audio clip: Adobe Flash Player (version 9 or above) is required to play this audio clip. Download the latest version here. You also need to have JavaScript enabled in your browser.

Java, Java, Java Java jing-jing-jing
Java, Java, Java Java jing-jing-jing

It’s not a cup of coffee but it’s hot as can be
Came pourin’ through the Gates on a “Big Mac” Nealy
Singin’, Java, Java, Java Java jing-jing-jing

Microsoft thought Java really could be a threat
Java through the Windows maybe put them in debt
Gates, he took a license but he altered the feel
Java members all said, “Bill, you’re outta the deal!”
Singin’, Java, Java, Java Java jing-jing-jing
Java, Java, Java Java jing-jing-jing

It’s like a cup of coffee ’cause it’s tasty and fresh
But it’s not really Java if the flavours don’t mesh
Pure Java, Java, Java Java jing-jing-jing

Microsoft released a browser, Java was there
The Sun, it rose and lit up what was really a dare
The RMI, the JNI were missing and lost
Scott said, “Bill, you broke your promise, Now pay the cost!”
Bill said, “Hey, my recipe is richer than yours”
Scott said, “I own the coffee shop, sit down and I’ll pour”
Pour Java, Java, Java Java jing-jing-jing
Java, Java, Java Java jing-jing-jing

Nobody can tell yet what the future may bring
All we know is Java goes jing-jing-jing
It goes Java, Java, Java Java jing-jing-jing
(Scott really means it)
Java, Java, Java Java jing-jing-jing
(Bill you better believe it)
Java, Java Java jing-jing-jing

Download the song here:
Java Posse Jingle

This song is the intro music of Java Posse podcast, written and performed in 1997 by Loose Bruce Kerr of the Dr. Demento Show and Sun Microsystems attorney.

“Nobody can tell yet what the future may bring” …. 13 years ago !!!

Cloud 20/20 Paper Presentation Contest – Third Place !!

It was a fantastic day at Bangalore. The Grand Finale of UNISYS Cloud 20/20 Technical Paper Presentation Contest was held at ITC Hotel yesterday. I was one of the finalists and I presented my paper on cloud computing to an audience of 400, which comprised of eminent personalities and stalwarts from the industry. I won the Third Place and was awarded a Nokia N97 mobile phone !!

It all started mid-November. A friend of mine, Venki, informed me about this contest on cloud computing. I went through the details and thought I could put some effort into it. I was not new to Cloud Computing since I had already conducted workshop on that topic in college. I got into action and learnt more about the topic and the challenges faced by this new computing paradigm. I decided to work on application development on the cloud. I came up with a topic: “Realizing Parallelism and Transparency in Applications Through Idempotence”. Wrote an abstract, submitted it, and waited for the results.

I was one among the sixty students shortlisted for the technical paper round. I had about a month to work on my technical paper. I browsed various papers and articles on the topic. Read about the current trends and what kind of applications cloud computing can expect in the future. I thus came up with a pretty decent technical paper, stating the problems and solutions. even though I did not have much hope of getting through to the next round, I eagerly awaited the results.

One evening I got a call telling that I am through to the telephone interview round. This news made me prepare myself well for the interview due to happen the next day. The telephone interview did not go well, since I was literally running and gasping for breath when my phone rang. I could not answer properly, even though I knew the answers. At the end of the day, I had lost all hopes.

But it was a pleasant surprise to see my name listed as one of the six finalists. I had to prepare a presentation for the finals. I worked a lot on it and prepared the slides. I flew to Bangalore and stayed at HM Suites, an excellent place.

The final round was on 15th. I met the other finalists. We got to know each other and became good friends. We had to present our paper to a panel of judges. The panel included eminent geniuses, Bob Supnik (CTO, UNISYS), Dr. Michael Salsburg (Chief Architect, UNISYS) and others. We all were a bit nervous. But the finals went on really well. Results were not announced until the next morning.

The Cloud 20/20 Grand Finale was a fabulous event. A lot of people from UNISYS, HP, Oracle, etc had been present. The entire day was packed with events, seminars and presentations. We were given a chance to present our papers to the audience, and the experience was really great. We were awarded the prizes by Bob Supnik. Deepak from IIIT-B won the first prize, an Apple Macbook Air Laptop. The second place was won by Kiran from IIIT-H, who got a Sony Vaio Laptop. I won the Third Place.

There was also a media event where the media was briefed about the entire event. Our names, I believe, appeared in quite a few papers. But I could get hold of Deccan Chronicle only.

Overall, it was a really great experience. And this was my first technical paper presentation. All thanks to UNISYS for organizing this event successfully and providing me an opportunity to explore more into the world of cloud computing.