Monday, July 16, 2007

Common mistakes of software developers (cont.)

Some of the common problems are listed:


Many designers and programmers refuse to listen to the experiences of others, claiming that their application is different, and of course much more complicated. Designers should be more open-minded about the similarities in their work. In response, ask “what is different in the LCD display software in a cellular phone versus one on a temperature controller? Are they really different?” Comparing control and communication systems side-by-side, both are characterized by modules that have inputs and outputs, with a function that maps the input to the output. A 256 by 256 image processed by a algorithm might not be very different from graphical code for a LCD dot matrix display of size 320 by 200. Furthermore, both use hardware with limited memory and processing power relative to the size of the application; both require development of software on a platform other than the target, and many of the issues in developing software for a micro-controller. The timing and volume of data is different. But if the system is designed correctly, these are just variables in equations. Methods to analyze resources such as memory and processing time are the same, both may require similar real-time scheduling, and both may also have high-speed interrupt handlers that can cause priority inversion. Perhaps if control systems and communication systems are similar, so are two different control applications or two different communication systems. Every application is unique, but more often than not the procedure to specify, designs, and build the software is the same. Embedded software designers should learn as much as possible from the experiences of others, and not shrug off experience just because it was acquired in a different application area.

Large if-then-else and case statements

It is not uncommon to see large if-else statements or case statements in embedded code. These are problematic from three perspectives

1.) They are extremely difficult to test, because code ends up having so many different paths. If statements are nested it becomes even more complicated.

2.). The difference between best-case and worst-case execution time becomes
significant. This leads either to under-utilizing the CPU, or possibilities of timing errors when the longest path is taken.

3.) The difficulty of structure code coverage testing grows exponentially with the number of branches, thus branches should be minimized.

This example confuses new testers who lack in programming experience.
Developers think their code is always correct and as mentioned earlier 99 % errors are corrected by themselves and remaining 1%.errors will be found out by testers. In the below example the

IF (0 < x < 12) then
SYSTEM.OUT.PRINTLN (“Month is” & i);
SYSTEM.OUT.PRINTLN (“Invalid input”);

Consider how this code could fail. Here are some of the simple programming errors that are very common mistakes that can go wrong:

a) Suppose the programmers said less than or equals instead of less than. The program would eject 0 as bad character. The only way to catch the error I by testing with 0.

b) If the code is written as less than 12 instead of less than or equal to 12, the program would go wrong.

“Testers with just the four boundary characters, /, 0, 9, and: will reveal every classification
Error that the programmer could make by getting an inequality wrong or by mistyping”

Error Handling:

Errors in dealing with errors are common. Error handling errors include failure to anticipate the possibility of errors and protect against them, failure to notice error conditions, and failure to deal with a detected error in a reasonable way. Many programmers correctly detect errors but then branch into untested error recovery routines. These routines’ bugs can cause more damage than the original problem.

Some times the errors are more even large while executing the tests and the Microsoft’s worst scenario is we can’t copy the error messages. There are some tools for copying the text of such error messages and also we can take the screen shots.


Testers should have a common sense in smelling the non obvious things. There is a relation between developers and testers in fixing the bugs. The probability of fixing the bugs is always depends on the way the test cases are communicated. Test cases play a major role in the QA's life. Test Cases are written in such a way that they are traceable, self contained and should not be duplicated in preparing they should always be atomic.

"Why go into something to test the waters? Go into it to make waves"