Re-Inventing Testing: What is Integration Testing? (Part 1)

(Thank you, Anne-Marie Charrett, for reviewing my work and helping with this post.)

One of the reasons I obsessively coach other testers is that they help me test my own expertise. Here is a particularly nice case of that, while working with a particularly bright and resilient student, Anita Gujrathi, (whose full name I am using here with her permission).

The topic was integration testing. I chose it from a list of skills Anita made for herself. It stood out because integration testing is one of those labels that everyone uses, yet few can define. Part of what I do with testers is help them become aware of things that they might think they know, yet may have only a vague intuition about. Once we identify those things, we can study and deepen that knowledge together.

Here is the start of our conversation (with minor edits for grammar and punctuation, and commentary in brackets):

What do you mean by integration testing?
[As I ask her this question I am simultaneously asking myself the same question. This is part of a process known as transpection. Also, I am not looking for “one right answer” but rather am exploring and exercising her thought processes, which is called the Socratic Method.]

Integration test is the test conducted when we are integrating two or more systems.
[This is not a wrong answer, but it is shallow, so I will press for more details.

By shallow, I mean that leaves out a lot of detail and nuances. A shallow answer may be fine in a lot of situations, but in coaching it is a black box that I must open.]

What do you mean by integrated?

That means kind of joining two systems such that they give and take data.
[This is a good answer but again it is shallow. She said “kind of” which I take as a signal that she may be not quite sure what words to use. I am wondering if she understands the technical aspects of how components are joined together during integration. For instance, when two systems share an operating space, they may have conflicting dependencies which may be discovered only in certain situations. I want to push for a more detailed answer in order to see what she knows about that sort of thing.]

What does it mean to join two systems?
[This process is called “driving to detail” or “drilling down”. I just keep asking for more depth in the answer by picking key ideas and asking what they mean. Sometimes I do this by asking for an example.]

For example, there is an application called WorldMate which processes the itineraries of the travellers and generates an XML file, and there is another application which creates the trip in its own format to track the travellers using that XML.
[Students will frequently give me an example when they don’t know how to explain a concept. They are usually hoping I will “get it” and thus release them from having to explain anything more. Examples are helpful, of course, but I’m not going to let her off the hook. I want to know how well she understands the concept of joining systems.

The interesting thing about this example is that it illustrates a weak form of integration– so weak that if she doesn’t understand the concept of integration well enough, I might be able to convince her that no integration is illustrated here.

What makes her example a case of weak integration is that the only point of contact between the two programs is a file that uses a standardized format. No other dependencies or mode of interaction is mentioned. This is exactly what designers do when they want to minimize interaction between components and eliminate risks due to integration.]

I still don’t know what it means to join two systems.
[This is because an example is not an explanation, and can never be an explanation. If someone asks what a flower is and you hold up a rose, they still know nothing about what a flower is, because you could hold up a rose in response to a hundred other such questions: what is a plant? what is a living thing? what is botany? what is a cell? what is red? what is carbon? what is a proton? what is your favorite thing? what is advertising? what is danger? Each time the rose is an answer to some specific aspect of the question, but not all aspects, but how do you know what the example of a rose actually refers to? Without an explanation, you are just guessing.]

I am coming to that. So, here we are joining WorldMate (which is third-party application) to my product so that when a traveller books a ticket from a service and receives the itinerary confirmation email, it then goes to WorldMate which generates XML to give it to my product. Thus, we have joined or created the communication between WorldMate and my application.
[It’s nice that Anita asserts herself, here. She sounds confident.

What she refers to is indeed communication, although not a very interesting form of communication in the context of integration risk. It’s not the sort of communication that necessarily requires integration testing, because the whole point of using XML structures is to cleanly separate two systems so that you don’t have to do anything special or difficult to integrate them.]

I still don’t see the answer to my question. I could just as easily say the two systems are not joined. But rather independent. What does join really mean?
[I am pretending not to see the answer in order to pressure her for more clarity. I won’t use this tactic as a coach unless I feel that the student is reasonably confident.]

Okay, basically when I say join I mean that we are creating the communication between the two systems
[This is the beginning of a good answer, but her example shows only a weak sort of communication.]

I don’t see any communication here. One creates an XML, the other reads it. Neither knows about the other.
[It was wrong of me to say I don’t see any communication. I should have said it was simplistic communication. What I was trying to do is provoke her to argue with me, but I regret saying it so strongly.]

It is a one-way communication.
[I agree it is one-way. That’s part of why I say it is a weak form of integration.]

Is Google integrated with Bing?
[One major tactic of the Socratic method is to find examples that seem to fit the student’s idea and yet refute what they were trying to prove. I am trying to test what Anita thinks is the difference between two things that are integrated and two things that are simply “nearby.”]

Ah no?

According to you, they are! Because I can Google something, then I can take the output and feed it to Bing, and Bing will do a search on that. I can Google for a business name and then paste the name into Bing and learn about the business. The example you gave is just an example of two independent programs that happen to deal with the same file.


So, if I test the two independent programs, haven’t I done all the testing that needs to be done? How is integration testing anything more or different or special?

At this point, Anita seems confused. This would be a good time to switch into lecture mode and help her get clarity. Or I could send her away to research the matter. But what I realized in that moment is that I was not satisfied with my own ideas about integration. When I asked myself “what would I say if I were her?” my answers sounded not much deeper than hers. I decided I needed to do some offline thinking about integration testing.

Lots of things in out world are slightly integrated. Some things are very integrated. This seems intuitively obvious, but what exactly is that difference? I’ve thought it through and I have answers now. Before I blog about it, what do you think?

86 thoughts on “Re-Inventing Testing: What is Integration Testing? (Part 1)

  1. I would say we have two types of integration.

    – Strongly integrated
    – Softly integrated

    In integration we can start by saying its a coupling of two things or objects. This coupling in software is the way information is passed from one object to another and or how it can be used. And how they are coupled reveals if its a strongly coupled object or loosely coupled.

    When I look at integration testing I first determine “can I get in-between the UI layer or under it, is there any way to expose it and what does it look like if it is exposed? If exposed what can I do with it? ”

    In a strongly integrated system, I can only test from endpoint to endpoint. I can’t access the communication layer with the exception of perhaps observing calls by capturing the calls as I stand in between. This is much more difficult to test as my access is limited and learning the circumstances that reveal interesting behavior is difficult. This also adds a layer of concern when code changes are made to one object as they can and often do directly affect the other which sets my teeth on edge trying to probe and observe for that interesting behavior.

    Whereas a more loosely coupled integration may offer the opportunity to mock or pretend to behave as the other object, something that I find useful when trying to test integration. Not to say this can’t be done in a more tightly coupled integration, but your ways to pry into the application are not as abundant.

    I think understanding how something is coupled, is the beginning of understanding integration testing.

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