110 CSIS - Lecture 33
Announcements: Quiz Next Wednesday. Includes material up to Wednesday, but not today. Since last quiz: 2D arrays, nested loops, user input validation, main, toString. Homework on class web site due Monday! Read: Chapter 6, sec 6.1 to 6.3. Testing When you work on your methods, does the code that you write work correctly the first time? What kinds of things are wrong? It doesn't compile you made a syntax error. For the most part, these are relatively easy to correct. It compiles and runs, but produces incorrect results your program has a logical error. These can be much harder to find. Experienced programmers don't make many syntax errors, and when they do they are able to correct them quickly. This is because the language details are familiar. But, they still make logical errors. In a large program it is extremely difficult to write a program that is 100% correct. Finding and correcting the defects in these programs is a serious challenge. What processes can we use to find defects? How do you go about finding problems? Three activities for improving the correctness of your programs: Testing: the process of finding out if an application or segment of code (such as a method) contains a bug. Doing a good job of testing is not easy there is much to think about when testing a program. Debugging: when testing shows that there is an error, you have to locate the error in the source code. You need to find out exactly what is causing the error. It can take a significant amount of work between knowing that there is an error and finding its cause. Writing for Maintainability: This is about following practices that lead to fewer errors in the first place. It is also about writing code so that errors are easier to find when they do occur. This is closely related to coding style and documentation. You want your code
to be easy to understand both for the original programmer and for someone else who might need to read it later. There is a huge difference between well written and poorly written code when it comes to debugging effort. [Ask question about what has been done in this class to encourage this practice] For now, we can divide testing up into 2 categories: Application testing and unit testing. Application Testing is testing that examines a complete application (program) for defects. In many cases, the tester does not have access to the code all testing is done through the user interface. Unit Testing tests smaller pieces of code (such as a method). Units can be items such as a class, a group of classes, or even a single method. Unit testing can be performed long before the application is complete. Let's look at application testing: The Triangle Application How can you go about determining if this program is correct? Well, you could just try random stuff and see what happens. How would you know if the program behaved correctly or not? You need to be more methodical. You need to define some test cases, where you try to verify whether the program behaves correctly for some particular characteristic. To do this, you need to understand what the program is supposed to do. Then you need to check if it actually does this thing. Programming Assignment This brings us to our next programming assignment The assignment has 2 parts. The first part is due next Friday, and does not involve any programming! Instead, I want you to test an application that I have written. The assignment is for you to write a program that encrypts messages. [Look at the application and the assignment. Discuss Caesar cipher] For example, you would want some tests to see if it builds the key square correctly. There are a bunch of rules that say how the program is supposed to do this. You need to come up with at least one test case for each rule. You should also think about: Positive testing making sure that the program behaves correctly when given good data
Negative testing making sure that the program handles incorrect data in a reasonable way. What do you think is the point of this assignment? Testing Unit What's unit testing? Testing parts of an application while you are building it: - it's never too early to start testing - Allows you to find problems earlier, when they are easier to fix - You build a set of tests, which you can reuse when you modify the code So, let's try some unit testing. Open up the diary-testing project from the chapter 6 folder. This is an early version of an appointment book. The final goal is to build an application that allows users to schedule appointments up to 1 year in advance. In this version, there are 3 classes: - Appointment: objects that keep track of an appointment's purpose and duration - Day: A Day object keeps track of a set of Appointments that have been made on a single day. Each day has a unique position in the year a value from 1 to 366. Appoints can only be made from 9AM to 5PM (using a 24 hour clock). - Week: Keeps track of the days in a week There are 2 simplifications in this project: appointments always start on an hour, and they always last for a multiple of 1 hour. Let's focus on the Day class how would we go about testing it? What kinds of questions do you have about the behavior of a Day object? - Does it have enough room to store the required number of appointments? - Doe the showAppointments method correctly display appointments that have been made? - Does the makeAppointment method correctly update the appointment field? - Does findSpace return the correct answer? We can answer all of these questions using the object bench and object inspectors. Create a Day object. Open the object inspector does the appointment field have enough elements to store the required number of appointments? Leave the object inspector open. One thing we want to do is make sure that objects behave correctly both when they are empty and when they are full. So, before we create any appointments we should make
sure that showAppointments works. Another element of good testing is to check boundaries this is where mistakes are often made. What are the boundaries of the Day object? - the first appt of the day - the last appt of the day Try to create 1 hour appointments at the beginning and end of the day. Also create one in the middle of the day. Use the inspector to make sure the appointments were created. Also call the showAppointments method Are there any other boundaries? Is there anything else we should check at the boundaries? Yes- want to make...