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Unit Testing in Java

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Defining a Unit

3:34 with Craig Dennis

What exactly is this unit we are testing?

Definitions

  • API - Application Programming Interface

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    There are different types of automated tested and 0:00
    as I originally stated we're gonna be focusing on unit testing. 0:02
    So that of course probably triggered you to ask the question, 0:07
    well what's this unit that's being tested? 0:09
    I'm glad you asked. 0:13
    A unit in this case is unfortunately one of those self contained definitions. 0:15
    The most definition used is this. 0:18
    Unit. 0:22
    The smallest testable part of an application. 0:22
    That's not a very satisfying answer, is it? 0:25
    I mean sometimes this is clear, but often times it's not. 0:27
    This lack of a proper definition definitely causes some confusion and, 0:31
    of course, arguments amongst developers. 0:35
    So how do you locate the smallest testable part? 0:39
    Well, a pretty straightforward logical approach to finding 0:42
    units in your application is to look at every publicly available method. 0:45
    In fact, most IDEs actually will do this for you. 0:50
    This is what they do when you create a test from a template. 0:53
    They'll build a single test for each method. 0:57
    However, this is one of those places where we developers have yet to be replaced. 1:00
    The code generation here doesn't actually understand our code, does it? 1:06
    It doesn't understand what it is that out code actually trying 1:09
    to accomplish, but we do. 1:12
    So here's the thing, let's define our unit test as testing a unit of work. 1:15
    Now a unit of work is something that causes publicly exposed 1:21
    behavior to occur for users of our code. 1:25
    Typically, you can gather the units of work by looking at the public facing API. 1:29
    An API, or Application Programming Interface, 1:34
    is the methods that have been publicly exposed to users of your code. 1:37
    Remember that when we declare methods public 1:43
    we're defining how we want those users to interact with our objects. 1:45
    And the beauty of that encapsulation is this. 1:49
    As long as the results are the same from each method, 1:52
    we're free to change the implementation however we want. 1:55
    Specifically, how we perform the requested behavior when the method is called. 1:58
    We might change the implementation by making the code cleaner. 2:03
    Maybe we'll make it faster, or have it use other existing code. 2:06
    But the point is this. 2:10
    The only guarantee to users of your code 2:11
    is that publicly exposed behavior will behave as you expect it will. 2:14
    And that's all we're really after, right? 2:20
    We want to find the publicly exposed behavior or units of work and 2:22
    ensure that it does indeed work the way that we intended. 2:26
    Whether that be a return value or an internal state change or 2:29
    even that misusing it causes an expected exception. 2:33
    So if we're only dealing with the public facing behavior, 2:37
    how do we ensure that all the private, magical code we have works? 2:41
    You know, we don't want to break the DRY practice, so 2:46
    we want to make reusable functions. 2:48
    And also, sometimes we don't want to expose the inner-workings of our object. 2:51
    So surely, there must be some way to work around this, right? 2:55
    Well, there is a better way. 2:59
    And in fact, just thinking about how to tackle testing public behavior, 3:00
    is gonna do just like I said earlier. 3:04
    It's gonna make us code better. 3:06
    It's going to drive home important programming concepts. 3:08
    Testing will help you code in a more professional manner. 3:12
    So, in order to get us there, 3:16
    it'll help us to have a more concrete example to work with. 3:18
    Thinking about programing in the abstract can sometimes feel overwhelming, and 3:21
    sometimes you just need to dive in. 3:25
    After a quick exercise let's do just that. 3:27
    Let's jump into the project for this course, 3:29
    which will help us explore these new concepts. 3:32

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