I am using choices in my HWUT test.
If in the command line, I don't specify the choice, then the test runs for all the choices.
And the test is run for each choice as per alphabetical order. But, I would the like the test to run the choices based on the order specified in the test file, as specified below.
For example:
printf("CHOICES: start, do_something, end");
I would like to it execute in the same order.
I did see some information regarding ordering of choices in this page.
This mentions about FIRST, NOT_LAST, NOT_FIRST, LAST. I couldn't figure out how to use this. Also, I'm not sure if this is the solution.
A HWUT Test's choice relates to a test that is completely independent. Your setup procedure must create a deterministic environment and the results must not depend on external things and must not depend on the history of HWUT tests!
If you have such a history dependency, then you must code the tests in a single choice (or, not having any choices at all).
Sometimes you 'make/build' things that are useful for all tests. For example, you might generate a huge database that is used by all CHOICES. When the last test finishes, the huge database shall be remove from the file system. Then, it makes sense to consider FIRST and LAST.
So, let us assume your case is case 3. Then, you check whether it is the first and/or last CHOICE by checking on argv[2] and argv[3] as described in the page that you reference.
/* Begin of 'main()' */
if( argc > 2 && strmp(argv[2], "FIRST") == 0 ) {
/* Build some stuff to be used by all CHOICES. */
}
... test current CHOICE ...
/* End of 'main()' */
if( argc > 3 && strmp(argv[3], "LAST") == 0 ) {
/* Delete some stuff that has been used by all CHOICES. */
}
If 'start' 'do_something', and 'end' must be executed in that order, then create three functions 'test_start(...)', 'test_do_something(...)', and 'test_end(...)' which execute your tests -- as suggested in item 2.
int main(int argc, char** argv)
{
...
test_start(...);
test_do_something(...);
test_end(...);
}
If something happens in 'start', 'do_domething', and 'end' that can be tested,
but testing all at once is too much for you, then
#include "hwut_unit.h"
int print_index = 0;
int main(int argc, char** argv)
{
...
hwut_if_choice("start") print_index = 0;
hwut_if_choice("do_something") print_index = 1;
hwut_if_choice("end") print_index = 2;
...
}
And in the 'test_start(...)' function do
void test_start(...)
{
...
if( print_index == 0 ) {
printf(...);
}
}
That is, make your print statements dependent on a 'print_index'.
The 'print_index' in turn must be set according to the CHOICE.
Related
I want to write a function in C and to put a condition in it. If the condition isn't met the program gives and error and prevents the user (developer) from compiling the code.
For example:
void func(int x)
{
if (x > 0)
{
//do stuff
}
else
{
//give an error and stops the code from compiling
}
}
prevents the user (developer) from compiling the code.
There's a problem there. You can decide on the user's behaviour, but you can't decide on the compilation of the program. If the code is right (right in the language sense, so it makes sense to the compiler), it will compile, else it won't. You can't make up new arbitrary rules for the compiler.
Before you can even run a program written in C, the compilation needs to be fulfilled.
Functions are called at run-time and so are the parameter values determined at run-time, too.
You can't make the compilation of your code dependent upon the variable x in C.
What you're trying to achieve is basically completely impossible.
Let's take an example. Assume that you want to manufacture an elevator, and you set the weight limit to 800 kilograms. You could build in something that makes the elevator stop if the weight exceeds the limit.
So take the scenario where we program the elevator so that it does not move if the weight limit is exceeded. That would typically be done with an assert() or something like that.
You could also in various way try to prevent this from happening, like making the elevator very small so that you cannot fit too many people. But that is not a fail safe option. We have restricted the volume, but nothing prevents a person from bringing a big chunk of solid gold into the elevator.
The point here is that you can measure the weight before moving the elevator, since this is done at runtime. But preventing someone from even trying to exceed the limit is virtually impossible.
In the general case, what you're asking for is completely impossible. What you can do is something like this:
void func(int x)
{
assert(x>0);
/* Do stuff */
}
And a slightly related thing that is possible is to create a test that is a part of the build process. You cannot prevent compilation the way you want, but you can use it to fail the whole build process. An example.
// main.c
int add(int x, int y)
{
return x+y;
}
bool test()
{
if(add(4,5) != 9) return false;
return true;
}
int main(int argc, char **argv)
{
if(strcmp(argv[1], "--test") == 0) {
if(!test()) {
printf("Test failed\n");
exit(EXIT_FAILURE);
}
// More tests
printf("All tests passed\n");
exit(EXIT_SUCCESS);
/* Rest of the main function */
}
Then you create a Makefile that compiles main.c and then calls ./a.out --test as a part of the build process. The above example is a very simple case, and for a more realistic case I would have made it a bit more sophisticated, but it shows how it can be done. Also, there are libraries that can take care of this kind of stuff, but this is a way to do it without having to use that.
Our organization has a required coding rule (without any explanation) that:
if … else if constructs should be terminated with an else clause
Example 1:
if ( x < 0 )
{
x = 0;
} /* else not needed */
Example 2:
if ( x < 0 )
{
x = 0;
}
else if ( y < 0 )
{
x = 3;
}
else /* this else clause is required, even if the */
{ /* programmer expects this will never be reached */
/* no change in value of x */
}
What edge case is this designed to handle?
What also concerns me about the reason is that Example 1 does not need an else but Example 2 does. If the reason is re-usability and extensibility, I think else should be used in both cases.
As mentioned in another answer, this is from the MISRA-C coding guidelines. The purpose is defensive programming, a concept which is often used in mission-critical programming.
That is, every if - else if must end with an else, and every switch must end with a default.
There are two reasons for this:
Self-documenting code. If you write an else but leave it empty it means: "I have definitely considered the scenario when neither if nor else if are true".
Not writing an else there means: "either I considered the scenario where neither if nor else if are true, or I completely forgot to consider it and there's potentially a fat bug right here in my code".
Stop runaway code. In mission-critical software, you need to write robust programs that account even for the highly unlikely. So you could see code like
if (mybool == TRUE)
{
}
else if (mybool == FALSE)
{
}
else
{
// handle error
}
This code will be completely alien to PC programmers and computer scientists, but it makes perfect sense in mission-critical software, because it catches the case where the "mybool" has gone corrupt, for whatever reason.
Historically, you would fear corruption of the RAM memory because of EMI/noise. This is not much of an issue today. Far more likely, memory corruption occurs because of bugs elsewhere in the code: pointers to wrong locations, array-out-of-bounds bugs, stack overflow, runaway code etc.
So most of the time, code like this comes back to slap yourself in the face when you have written bugs during the implementation stage. Meaning it could also be used as a debug technique: the program you are writing tells you when you have written bugs.
EDIT
Regarding why else is not needed after every single if:
An if-else or if-else if-else completely covers all possible values that a variable can have. But a plain if statement is not necessarily there to cover all possible values, it has a much broader usage. Most often you just wish to check a certain condition and if it is not met, then do nothing. Then it is simply not meaningful to write defensive programming to cover the else case.
Plus it would clutter up the code completely if you wrote an empty else after each and every if.
MISRA-C:2012 15.7 gives no rationale why else is not needed, it just states:
Note: a final else statement is not required for a simple if
statement.
Your company followed MISRA coding guidance. There are a few versions of these guidelines that contain this rule, but from MISRA-C:2004†:
Rule 14.10 (required): All if … else if constructs shall be terminated
with an else clause.
This rule applies whenever an if statement is followed by one or more
else if statements; the final else if shall be followed by an else
statement. In the case of a simple if statement then the else
statement need not be included. The requirement for a final else
statement is defensive programming. The else statement shall either
take appropriate action or contain a suitable comment as to why no
action is taken. This is consistent with the requirement to have a
final default clause in a switch statement. For example this code
is a simple if statement:
if ( x < 0 )
{
log_error(3);
x = 0;
} /* else not needed */
whereas the following code demonstrates an if, else if construct
if ( x < 0 )
{
log_error(3);
x = 0;
}
else if ( y < 0 )
{
x = 3;
}
else /* this else clause is required, even if the */
{ /* programmer expects this will never be reached */
/* no change in value of x */
}
In MISRA-C:2012, which supersedes the 2004 version and is the current recommendation for new projects, the same rule exists but is numbered 15.7.
Example 1:
in a single if statement programmer may need to check n number of conditions and performs single operation.
if(condition_1 || condition_2 || ... condition_n)
{
//operation_1
}
In a regular usage performing a operation is not needed all the time when if is used.
Example 2:
Here programmer checks n number of conditions and performing multiple operations. In regular usage if..else if is like switch you may need to perform a operation like default. So usage else is needed as per misra standard
if(condition_1 || condition_2 || ... condition_n)
{
//operation_1
}
else if(condition_1 || condition_2 || ... condition_n)
{
//operation_2
}
....
else
{
//default cause
}
† Current and past versions of these publications are available for purchase via the MISRA webstore (via).
This is the equivalent of requiring a default case in every switch.
This extra else will Decrease code coverage of your program.
In my experience with porting linux kernel , or android code to different platform many time we do something wrong and in logcat we see some error like
if ( x < 0 )
{
x = 0;
}
else if ( y < 0 )
{
x = 3;
}
else /* this else clause is required, even if the */
{ /* programmer expects this will never be reached */
/* no change in value of x */
printk(" \n [function or module name]: this should never happen \n");
/* It is always good to mention function/module name with the
logs. If you end up with "this should never happen" message
and the same message is used in many places in the software
it will be hard to track/debug.
*/
}
Only a brief explanation, since I did this all about 5 years ago.
There is (with most languages) no syntactic requirement to include "null" else statement (and unnecessary {..}), and in "simple little programs" there is no need. But real programmers don't write "simple little programs", and, just as importantly, they don't write programs that will be used once and then discarded.
When one write an if/else:
if(something)
doSomething;
else
doSomethingElse;
it all seems simple and one hardly sees even the point of adding {..}.
But some day, a few months from now, some other programmer (you would never make such a mistake!) will need to "enhance" the program and will add a statement.
if(something)
doSomething;
else
doSomethingIForgot;
doSomethingElse;
Suddenly doSomethingElse kinda forgets that it's supposed to be in the else leg.
So you're a good little programmer and you always use {..}. But you write:
if(something) {
if(anotherThing) {
doSomething;
}
}
All's well and good until that new kid makes a midnight modification:
if(something) {
if(!notMyThing) {
if(anotherThing) {
doSomething;
}
else {
dontDoAnything; // Because it's not my thing.
}}
}
Yes, it's improperly formatted, but so is half the code in the project, and the "auto formatter" gets bollixed up by all the #ifdef statements. And, of course, the real code is far more complicated than this toy example.
Unfortunately (or not), I've been out of this sort of thing for a few years now, so I don't have a fresh "real" example in mind -- the above is (obviously) contrived and a bit hokey.
This, is done to make the code more readable, for later references and to make it clear, to a later reviewer, that the remaining cases handled by the last else, are do nothing cases, so that they are not overlooked somehow at first sight.
This is a good programming practice, which makes code reusable and extend-able.
I would like to add to – and partly contradict – the previous answers. While it is certainly common to use if-else if in a switch-like manner that should cover the full range of thinkable values for an expression, it is by no means guaranteed that any range of possible conditions is fully covered. The same can be said about the switch construct itself, hence the requirement to use a default clause, which catches all remaining values and can, if not otherwise required anyway, be used as an assertion safeguard.
The question itself features a good counter-example: The second condition does not relate to x at all (which is the reason why I often prefer the more flexible if-based variant over the switch-based variant). From the example it is obvious that if condition A is met, x should be set to a certain value. Should A not be met, then condition B is tested. If it is met, then x should receive another value. If neither A nor B are met, then x should remain unchanged.
Here we can see that an empty else branch should be used to comment on the programmer's intention for the reader.
On the other hand, I cannot see why there must be an else clause especially for the latest and innermost if statement. In C, there is no such thing as an 'else if'. There is only if and else. Instead, the construct should formally be indented this way (and I should have put the opening curly braces on their own lines, but I don't like that):
if (A) {
// do something
}
else {
if (B) {
// do something else (no pun intended)
}
else {
// don't do anything here
}
}
Should any standard happen to require curly braces around every branch, then it would contradict itself if it mentioned "if ... else if constructs" at the same time.
Anyone can imagine the ugliness of deeply nested if else trees, see here on a side note. Now imagine that this construct can be arbitrarily extended anywhere. Then asking for an else clause in the end, but not anywhere else, becomes absurd.
if (A) {
if (B) {
// do something
}
// you could to something here
}
else {
// or here
if (B) { // or C?
// do something else (no pun intended)
}
else {
// don't do anything here, if you don't want to
}
// what if I wanted to do something here? I need brackets for that.
}
In the end, it comes down for them to defining precisely what is meant with an "if ... else if construct"
The basic reason is probably code coverage and the implicit else: how will the code behave if the condition is not true? For genuine testing, you need some way to see that you have tested with the condition false. If every test case you have goes through the if clause, your code could have problems in the real world because of a condition that you did not test.
However, some conditions may properly be like Example 1, like on a tax return: "If the result is less than 0, enter 0." You still need to have a test where the condition is false.
Logically any test implies two branches. What do you do if it is true, and what do you do if it is false.
For those cases where either branch has no functionality, it is reasonable to add a comment about why it doesn't need to have functionality.
This may be of benefit for the next maintenance programmer to come along. They should not have to search too far to decide if the code is correct. You can kind of Prehunt the Elephant.
Personally, it helps me as it forces me to look at the else case, and evaluate it. It may be an impossible condition, in which case i may throw an exception as the contract is violated. It may be benign, in which case a comment may be enough.
Your mileage may vary.
Most the time when you just have a single if statement, it's probably one of reasons such as:
Function guard checks
Initialization option
Optional processing branch
Example
void print (char * text)
{
if (text == null) return; // guard check
printf(text);
}
But when you do if .. else if, it's probably one of reasons such as:
Dynamic switch-case
Processing fork
Handling a processing parameter
And in case your if .. else if covers all possibilities, in that case your last if (...) is not needed, you can just remove it, because at that point the only possible values are the ones covered by that condition.
Example
int absolute_value (int n)
{
if (n == 0)
{
return 0;
}
else if (n > 0)
{
return n;
}
else /* if (n < 0) */ // redundant check
{
return (n * (-1));
}
}
And in most of these reasons, it's possible something doesn't fit into any of the categories in your if .. else if, thus the need to handle them in a final else clause, handling can be done through business-level procedure, user notification, internal error mechanism, ..etc.
Example
#DEFINE SQRT_TWO 1.41421356237309504880
#DEFINE SQRT_THREE 1.73205080756887729352
#DEFINE SQRT_FIVE 2.23606797749978969641
double square_root (int n)
{
if (n > 5) return sqrt((double)n);
else if (n == 5) return SQRT_FIVE;
else if (n == 4) return 2.0;
else if (n == 3) return SQRT_THREE;
else if (n == 2) return SQRT_TWO;
else if (n == 1) return 1.0;
else if (n == 0) return 0.0;
else return sqrt(-1); // error handling
}
This final else clause is quite similar to few other things in languages such as Java and C++, such as:
default case in a switch statement
catch(...) that comes after all specific catch blocks
finally in a try-catch clause
Our software was not mission critical, yet we also decided to use this rule because of defensive programming.
We added a throw exception to the theoretically unreachable code (switch + if-else). And it saved us many times as the software failed fast e.g. when a new type has been added and we forgot to change one-or-two if-else or switch. As a bonus it made super easy to find the issue.
Well, my example involves undefined behavior, but sometimes some people try to be fancy and fails hard, take a look:
int a = 0;
bool b = true;
uint8_t* bPtr = (uint8_t*)&b;
*bPtr = 0xCC;
if(b == true)
{
a += 3;
}
else if(b == false)
{
a += 5;
}
else
{
exit(3);
}
You probably would never expect to have bool which is not true nor false, however it may happen. Personally I believe this is problem caused by person who decides to do something fancy, but additional else statement can prevent any further issues.
I'm currently working with PHP. Creating a registration form and a login form. I am just purely using if and else. No else if or anything that is unnecessary.
If user clicks submits button -> it goes to the next if statement... if username is less than than 'X' amount of characters then alert. If successful then check password length and so on.
No need for extra code such as an else if that could dismiss reliability for server load time to check all the extra code.
As this question on boolean if/else if was closed as a duplicate. As well, there are many bad answers here as it relates to safety-critical.
For a boolean, there are only two cases. In the boolean instance, following the MISRA recommendation blindly maybe bad. The code,
if ( x == FALSE ) {
// Normal action
} else if (x == TRUE ) {
// Fail safe
}
Should just be refactored to,
if ( x == FALSE ) {
// Normal action
} else {
// Fail safe
}
Adding another else increases cyclometric complexity and makes it far harder to test all branches. Some code maybe 'safety related'; Ie, not a direct control function that can cause an unsafe event. In this code, it is often better to have full testability without instrumentation.
For truly safety functional code, it might make sense to separate the cases to detect a fault in this code and have it reported. Although I think logging 'x' on the failure would handle both. For the other cases, it will make the system harder to test and could result in lower availability depending on what the second 'error handling' action is (see other answers where exit() is called).
For non-booleans, there may be ranges that are nonsensical. Ie, they maybe some analog variable going to a DAC. In these cases, the if(x > 2) a; else if(x < -2) b; else c; makes sense for cases where deadband should not have been sent, etc. However, these type of cases do not exist for a boolean.
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I am new to programming and this one has me baffled.
I am writing a function to be called by main that takes the command line arguments and stores them in a struct to use later. This specific example is for use with image editing, but can be used anywhere.
Desired performance: Function takes arguments from the command line. Three specific arguments are identified and checked for: -h, -o and -t. If present they will alter the struct values. Arguments -o and -t store the arguments immediately following them into their respective struct fields. Any argument that is not -h or does not have -o or -t preceding it is assumed to be the input file name and stored in flag->inputFile. If all arguments are accounted for, then flag->inputFile should remain NULL and can be tested for in the main function and program terminated if this is true.
Problem: When there is no input file specified (using the above parameters) flag->inputFile keeps getting set to -o when it is included as an argument.
Solution: Thanks to Scott this question has been answered by replacing several if statements with else if has now seemed to fix the problem, and the function appears to be working as desired.
My understanding of what was happening is that the else statement was being run in every iteration of i unless the -t argument was included, since it was the statement immediately before the else
The compiler I'm using is gcc and this is my code. (I know my struct is not packed, I'm still trying to get my head around this and can't see how it would result in what I'm seeing. Segmentation fault, yes, but not this?)
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
struct PROMPTFLAGS {
int help; // Change from NULL if -h argument present
char * outputFile; // Store argument after -o as the output file
char * inputFile; // Argument not paired with a flag stored here as input file
float threshold; // Stores a value to use in image manipulation in main
};
struct PROMPTFLAGS * parsargs(int argc, char * argv[]) {
struct PROMPTFLAGS* flag = malloc(sizeof(struct PROMPTFLAGS));
int i;
printf("argc: %d\n",argc);
for (i = 1; i < argc; i++) {
char * arg = argv[i];
int str_aft = i+1; // Allows the next string to be used in this iteration of the loop
if (strcmp(arg,"-h") == 0) {
flag->help = 1;
}
if (strcmp(arg,"-o") == 0) { // Changing this to 'else if' seems to be a fix
flag->outputFile = argv[str_aft];
i++; // Skips over next arg since already read by argv[str_aft]
}
if (strcmp(arg,"-t") == 0) { // Changing this to 'else if' seems to be a fix
flag->threshold = strtod(argv[str_aft],NULL);
i++; // Skips over next arg since already read by argv[str_aft]
}
else {
flag->inputFile = arg;
}
}
return flag;
}
int main(int argc, char* argv[]) {
struct PROMPTFLAGS * flags;
flags = parsargs(argc, argv);
printf("Help = %d\n",flags.help);
printf("Output = %s\n",flags.outputFile);
printf("Input = %s\n",flags.inputFile);
printf("Threshold = %s\n",flags.threshold);
return 0;
}
I apologise for the poor format of the first version of this question and hope that this edit is better. I have made the functions' desired outcomes and the problem I encountered clearer and removed most of the test prints I had through the code and added some comments. I have also included the solution to my problem (provided by another user) and my understanding of what was happening in the broken code.
If people still think this is a poor question or of no use to anyone else then I'm happy to take it down, but have edited and left it up hoping it can help someone else.
This is my first post on stack overflow and I thank everyone for their help and patience while I learn to code and the best manner to post questions.
You set flag->inputFile = arg whenever arg is not "-t" (the else after testing for "-t"). I'm not sure when you want to assign to this field, but I am sure this isn't the right logic for it. For example, if you wanted to do this when arg is none of the other specific flags you are looking for, you should be using if ... else if ... else if ... else.
I'm wanting to get a list of supplementary groups for the user by sending a request through NSS. To my reckoning, the following program should let me enumerate all the groups (so I can then compare members):
#include <stdio.h>
#include <grp.h>
#include <stdlib.h>
struct group *groupStruct;
int main(){
setgrent();
while ( groupStruct=getgrent() )
printf("%s\n", groupStruct->gr_name);
endgrent();
return 0;
}
I'm basing this assumption on this part of the source code for id that gets executed with id -Gn (since that's the functionality I want to replicate). Looking at that it looks like it gets the list of groups via getugroups (0, NULL, username, gid) with getugroups() being defined in another file (essentially the same code found here). It looks like that is going through the same setgrent()/getgrent() procedure as above, so my feeling is that my simple program ought to enumerate the system's groups (instead, it only does the groups in /etc/group but I have winbind on this machine and id -Gn pulls in the winbind groups the user is a member of).
For posterity:
I still don't know why the id -Gn code works but not mine, but I think I fixed my own issue after a lot of back and forth. Basically I'm building a shared object and enumerating their current memberships by way of a helper program that uses initgroups/getgroups to set the running processes's (the helper executable) persona to the target user's default persona (what they would get after logging in. This is the full code of the helper program:
#include <stdio.h>
#include <unistd.h>
struct group *groupStruct;
int main(int argc, char *argv[]){
int numgroups, iter, retCode;
int numgroups_max = sysconf(_SC_NGROUPS_MAX) + 1;
gid_t groupList[numgroups_max];
if (argc != 2){
printf("Insufficient Arguments.\n");
return 1;
}
retCode=initgroups(argv[1], 0);
if (retCode != 0){
printf("Unspecified failure: %d\n\n", retCode);
return 1;
}
numgroups = getgroups(numgroups_max, groupList);
for (iter=0; iter <= numgroups; iter++){
if (iter != 0 && iter != numgroups )
printf(" ");
// "zero" means both "nothing more" and could be the root user's primary group, allow the first one through
if ( groupList[iter] == 0 && getuid() == 0 ){
if ( iter != 0 )
break;
}else if ( groupList[iter] == 0 )
break;
printf("%d", groupList[iter]);
}
return 0;
}
Username is hard coded just for testing purposes. After compiling and testing it produces the group ID's for the user. Changing the hard coded value (or pushing it into argv) resolves the problem. I pushed this into a helper executable because it's changing the running process's persona (at least the group membership portion).
I'll probably move it into the library's calling routine for performance/security (I can save the supplementary and primary groups before with getgroups and setgroups), but it was quicker for me to do a proof of concept in a separate executable.
I've started to dig into the GLib documentation and discovered that it also offers a unit testing framework.
But how could you do unit tests in a procedural language? Or does it require to program OO in C?
Unit testing only requires "cut-planes" or boundaries at which testing can be done. It is quite straightforward to test C functions which do not call other functions, or which call only other functions that are also tested. Some examples of this are functions which perform calculations or logic operations, and are functional in nature. Functional in the sense that the same input always results in the same output. Testing these functions can have a huge benefit, even though it is a small part of what is normally thought of as unit testing.
More sophisticated testing, such as the use of mocks or stubs is also possible, but it is not nearly as easy as it is in more dynamic languages, or even just object oriented languages such as C++. One way to approach this is to use #defines. One example of this is this article, Unit testing OpenGL applications, which shows how to mock out OpenGL calls. This allows you to test that valid sequences of OpenGL calls are made.
Another option is to take advantage of weak symbols. For example, all MPI API functions are weak symbols, so if you define the same symbol in your own application, your implementation overrides the weak implementation in the library. If the symbols in the library weren't weak, you would get duplicate symbol errors at link time. You can then implement what is effectively a mock of the entire MPI C API, which allows you to ensure that calls are matched up properly and that there aren't any extra calls that could cause deadlocks. It is also possible to load the library's weak symbols using dlopen() and dlsym(), and pass the call on if necessary. MPI actually provides the PMPI symbols, which are strong, so it is not necessary to use dlopen() and friends.
You can realize many of the benefits of unit testing for C. It is slightly harder, and it may not be possible to get the same level of coverage you might expect from something written in Ruby or Java, but it's definitely worth doing.
At the most basic level, unit tests are just bits of code that execute other bits of code and tell you if they worked as expected.
You could simply make a new console app, with a main() function, that executed a series of test functions. Each test would call a function in your app and return a 0 for success or another value for failure.
I'd give you some example code, but I'm really rusty with C. I'm sure there are some frameworks out there that would make this a little easier too.
You can use libtap which provides a number of functions which can provide diagnostics when a test fails. An example of its use:
#include <mystuff.h>
#include <tap.h>
int main () {
plan(3);
ok(foo(), "foo returns 1");
is(bar(), "bar", "bar returns the string bar");
cmp_ok(baz(), ">", foo(), "baz returns a higher number than foo");
done_testing;
}
Its similar to tap libraries in other languages.
Here's an example of how you would implement multiple tests in a single test program for a given function that might call a library function.
Suppose we want to test the following module:
#include <stdlib.h>
int my_div(int x, int y)
{
if (y==0) exit(2);
return x/y;
}
We then create the following test program:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <setjmp.h>
// redefine assert to set a boolean flag
#ifdef assert
#undef assert
#endif
#define assert(x) (rslt = rslt && (x))
// the function to test
int my_div(int x, int y);
// main result return code used by redefined assert
static int rslt;
// variables controling stub functions
static int expected_code;
static int should_exit;
static jmp_buf jump_env;
// test suite main variables
static int done;
static int num_tests;
static int tests_passed;
// utility function
void TestStart(char *name)
{
num_tests++;
rslt = 1;
printf("-- Testing %s ... ",name);
}
// utility function
void TestEnd()
{
if (rslt) tests_passed++;
printf("%s\n", rslt ? "success" : "fail");
}
// stub function
void exit(int code)
{
if (!done)
{
assert(should_exit==1);
assert(expected_code==code);
longjmp(jump_env, 1);
}
else
{
_exit(code);
}
}
// test case
void test_normal()
{
int jmp_rval;
int r;
TestStart("test_normal");
should_exit = 0;
if (!(jmp_rval=setjmp(jump_env)))
{
r = my_div(12,3);
}
assert(jmp_rval==0);
assert(r==4);
TestEnd();
}
// test case
void test_div0()
{
int jmp_rval;
int r;
TestStart("test_div0");
should_exit = 1;
expected_code = 2;
if (!(jmp_rval=setjmp(jump_env)))
{
r = my_div(2,0);
}
assert(jmp_rval==1);
TestEnd();
}
int main()
{
num_tests = 0;
tests_passed = 0;
done = 0;
test_normal();
test_div0();
printf("Total tests passed: %d\n", tests_passed);
done = 1;
return !(tests_passed == num_tests);
}
By redefining assert to update a boolean variable, you can continue on if an assertion fails and run multiple tests, keeping track of how many succeeded and how many failed.
At the start of each test, set rslt (the variables used by the assert macro) to 1, and set any variables that control your stub functions. If one of your stubs gets called more than once, you can set up arrays of control variables so that the stubs can check for different conditions on different calls.
Since many library functions are weak symbols, they can be redefined in your test program so that they get called instead. Prior to calling the function to test, you can set a number of state variables to control the behavior of the stub function and check conditions on the function parameters.
In cases where you can't redefine like that, give the stub function a different name and redefine the symbol in the code to test. For example, if you want to stub fopen but find that it isn't a weak symbol, define your stub as my_fopen and compile the file to test with -Dfopen=my_fopen.
In this particular case, the function to be tested may call exit. This is tricky, since exit can't return to the function being tested. This is one of the rare times when it makes sense to use setjmp and longjmp. You use setjmp before entering the function to test, then in the stubbed exit you call longjmp to return directly back to your test case.
Also note that the redefined exit has a special variable that it checks to see if you actually want to exit the program and calls _exit to do so. If you don't do this, your test program may not quit cleanly.
This test suite also counts the number of attempted and failed tests and returns 0 if all tests passed and 1 otherwise. That way, make can check for test failures and act accordingly.
The above test code will output the following:
-- Testing test_normal ... success
-- Testing test_div0 ... success
Total tests passed: 2
And the return code will be 0.
There is nothing intrinsically object-oriented about testing small pieces of code in isolation. In procedural languages you test functions and collections thereof.
If you are desperate, and you'd have to be desperate, I banged together a little C preprocessor and gmake based framework. It started as a toy, and never really grew up, but I have used it to develop and test a couple of medium sized (10,000+ line) projects.
Dave's Unit Test is minimally intrusive yet it can do some tests I had originally thought would not be possible for a preprocessor based framework (you can demand that a certain stretch of code throw a segmentation fault under certain conditions, and it will test it for you).
It is also an example of why making heavy use of the preprocessor is hard to do safely.
The simplest way of doing a unit test is to build a simple driver code that gets linked with the other code, and call each function in each case...and assert the values of the results of the functions and build up bit by bit...that's how I do it anyway
int main(int argc, char **argv){
// call some function
int x = foo();
assert(x > 1);
// and so on....
}
Hope this helps.
With C it must go further than simply implementing a framework on top of existing code.
One thing I've always done is make a testing module (with a main) that you can run little tests from to test your code. This allows you to do very small increments between code and test cycles.
The bigger concern is writing your code to be testable. Focus on small, independent functions that do not rely on shared variables or state. Try writing in a "Functional" manner (without state), this will be easier to test. If you have a dependency that can't always be there or is slow (like a database), you may have to write an entire "mock" layer that can be substituted for your database during tests.
The principle unit testing goals still apply: ensure the code under test always resets to a given state, test constantly, etc...
When I wrote code in C (back before Windows) I had a batch file that would bring up an editor, then when I was done editing and exited, it would compile, link, execute tests and then bring up the editor with the build results, test results and the code in different windows. After my break (a minute to several hours depending on what was being compiled) I could just review results and go straight back to editing. I'm sure this process could be improved upon these days :)
I use assert. It's not really a framework though.
You can write a simple minimalistic test framework yourself:
// test_framework.h
#define BEGIN_TESTING int main(int argc, char **argv) {
#define END_TESTING return 0;}
#define TEST(TEST_NAME) if (run_test(TEST_NAME, argc, argv))
int run_test(const char* test_name, int argc, char **argv) {
// we run every test by default
if (argc == 1) { return 1; }
// else we run only the test specified as a command line argument
for (int i = 1; i < argc; i++) {
if (!strcmp(test_name, argv[i])) { return 0; }
}
return 0;
}
Now in the actual test file do this:
#include test_framework.h
BEGIN_TESTING
TEST("MyPassingTest") {
assert(1 == 1);
}
TEST("MyFailingTest") {
assert(1 == 2);
}
END_TESTING
If you want to run all tests, execute ./binary without command line arguments, if you want to run just a particular test, execute ./binary MyFailingTest