第9章ソフトウェア工学

Usability and acceptance testing are quite different. Let’s consider again the software for the lane departure systems (LDS) that are incorporated into automobiles these days. Acceptance testing would confirm that the lane departure system works as expected: Did the warning happen when a vehicle crossed a lane line? Did the software recognize when the vehicle departed the lane? Did the system warning start and end in an amount of time that was appropriate to the user? When the system is disabled, did the software ignore lane departures and not trigger the warnings?

With usability testing, the focus is more on whether the system met the expectations of the users interacting with it: Was the system usable? Did the user use the feature as intended? Did the user react appropriately to the warning signal? Was the signal so startling it caused the user to jerk and risk an accident? Did the user simply turn off the system because they found it annoying? The focus of usability testing is on how the solution is being used and whether it was created in the most intuitive manner

The Insurance Institute for Highway Safety found that 49% of users turned the LDS off during their normal commuting. More important, it was found that 54% turned it on if it used tactile warnings compared to only 46% turning it on if it used an audible alert. From a usability testing standpoint, this shows that it is better to focus on a tactile warning over an audible one if the goal is to get the most usage. Because LDS has been shown to decrease the chance of fatal accidents, even with low usage, it can still help save lives.

Software developers use many tools that facilitate development; some of them are used daily while others only occasionally, but they all play an important role in software engineering process.

A compiler is a program that converts source code into a syntax or format that a computer can execute. Programming languages such as C and C++ compile into machine code, which consists of instructions for a specific processor. Other programming languages such as Java compile into machine independent code. For example, Java program code is generally compiled into Java bytecode. This machine independent code is then executed on a Java Virtual Machine.

A debugger is a program that assists in detecting and correcting of bugs. It typically helps in finding issues in code by enabling features such as the ability to halt a program while it’s running so that variable values can be displayed and even changed. Debuggers can also run a program line by line to see what each line of code is doing. More advanced features involve halting a program on a specified condition and checking for deadlock and memory leaks. Figure 9.21 shows the NetBeans debugger stopped on line 6 of a program. In the lower part of the screen, the software developer can see the values of the variables currently used by the program.

A profiler is a program that performs dynamic program analysis that can be used to optimize or otherwise streamline code. It collects data such as frequency and duration of method calls and presents it to the software developer who can use it to propose code optimizations. The process of data gathering is called profiling, and it is typically performed when the performance of the software system does not meet specified criteria.

Software engineers typically write source code in an IDE such as IntelliJ, Microsoft Visual Studio, or VS Code. An IDE is a software application that facilitates software development by combining several tools that developers use such as an editor, compiler, debugger, and profiler. Some IDEs only support a specific programming language, such as IDLE for Python, and some support multiple programming languages, such as Microsoft Visual Studio, which supports C++, C#, Visual Basic, and J#.

The best IDEs provide features that facilitate writing and maintaining source code. These features can span from simple features such as syntax highlighting to sophisticated ones such as static analysis of source code. Syntax highlighting displays different parts of the source code in different colors, which facilitates reading. Figure 9.22 shows an IDE highlighting Java code.

The cost of IDEs can range from free to thousands of dollars. IDEs such as Eclipse, NetBeans, and Microsoft Visual Studio Code are free. Microsoft Visual Studio and IntelliJ IDEA have a fee associated, although there are free editions of each available. Generally, the cost of an IDE is offset by the increase in productivity that a developer gains from its use.