File: autoconf.info,  Node: Guidelines,  Next: Test Functions,  Up: Writing Test Programs

6.2.1 Guidelines for Test Programs
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The most important rule to follow when writing testing samples is:

                          _Look for realism._

   This motto means that testing samples must be written with the same
strictness as real programs are written.  In particular, you should
avoid "shortcuts" and simplifications.

   Don't just play with the preprocessor if you want to prepare a
compilation.  For instance, using ‘cpp’ to check whether a header is
functional might let your ‘configure’ accept a header which causes some
_compiler_ error.  Do not hesitate to check a header with other headers
included before, especially required headers.

   Make sure the symbols you use are properly defined, i.e., refrain
from simply declaring a function yourself instead of including the
proper header.

   Test programs should not write to standard output.  They should exit
with status 0 if the test succeeds, and with status 1 otherwise, so that
success can be distinguished easily from a core dump or other failure;
segmentation violations and other failures produce a nonzero exit
status.  Unless you arrange for ‘exit’ to be declared, test programs
should ‘return’, not ‘exit’, from ‘main’, because on many systems ‘exit’
is not declared by default.

   Test programs can use ‘#if’ or ‘#ifdef’ to check the values of
preprocessor macros defined by tests that have already run.  For
example, if you call ‘AC_HEADER_STDBOOL’, then later on in
‘configure.ac’ you can have a test program that includes ‘stdbool.h’
conditionally:

     #ifdef HAVE_STDBOOL_H
     # include 
     #endif

   Both ‘#if HAVE_STDBOOL_H’ and ‘#ifdef HAVE_STDBOOL_H’ will work with
any standard C compiler.  Some developers prefer ‘#if’ because it is
easier to read, while others prefer ‘#ifdef’ because it avoids
diagnostics with picky compilers like GCC with the ‘-Wundef’ option.

   If a test program needs to use or create a data file, give it a name
that starts with ‘conftest’, such as ‘conftest.data’.  The ‘configure’
script cleans up by running ‘rm -f -r conftest*’ after running test
programs and if the script is interrupted.