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(autoconf.info)Test Functions

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Test Functions
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   Function declarations in test programs should have a prototype
conditionalized for C++.  In practice, though, test programs rarely need
functions that take arguments.

     #ifdef __cplusplus
     foo(int i)
     #else
     foo(i) int i;
     #endif

   Functions that test programs declare should also be conditionalized
for C++, which requires `extern "C"' prototypes.  Make sure to not
include any header files containing clashing prototypes.

     #ifdef __cplusplus
     extern "C" void *malloc(size_t);
     #else
     char *malloc();
     #endif

   If a test program calls a function with invalid parameters (just to
see whether it exists), organize the program to ensure that it never
invokes that function.  You can do this by calling it in another
function that is never invoked.  You can't do it by putting it after a
call to `exit', because GCC version 2 knows that `exit' never returns
and optimizes out any code that follows it in the same block.

   If you include any header files, make sure to call the functions
relevant to them with the correct number of arguments, even if they are
just 0, to avoid compilation errors due to prototypes.  GCC version 2
has internal prototypes for several functions that it automatically
inlines; for example, `memcpy'.  To avoid errors when checking for
them, either pass them the correct number of arguments or redeclare them
with a different return type (such as `char').