File: autoconf.info,  Node: Writing Tests,  Next: Results,  Prev: Existing Tests,  Up: Top

6 Writing Tests
***************

If the existing feature tests don't do something you need, you have to
write new ones.  These macros are the building blocks.  They provide
ways for other macros to check whether various kinds of features are
available and report the results.

   This chapter contains some suggestions and some of the reasons why
the existing tests are written the way they are.  You can also learn a
lot about how to write Autoconf tests by looking at the existing ones.
If something goes wrong in one or more of the Autoconf tests, this
information can help you understand the assumptions behind them, which
might help you figure out how to best solve the problem.

   These macros check the output of the compiler system of the current
language (*note Language Choice::).  They do not cache the results of
their tests for future use (*note Caching Results::), because they don't
know enough about the information they are checking for to generate a
cache variable name.  They also do not print any messages, for the same
reason.  The checks for particular kinds of features call these macros
and do cache their results and print messages about what they're
checking for.

   When you write a feature test that could be applicable to more than
one software package, the best thing to do is encapsulate it in a new
macro.  *Note Writing Autoconf Macros::, for how to do that.

* Menu:

* Language Choice::             Selecting which language to use for testing
* Writing Test Programs::       Forging source files for compilers
* Running the Preprocessor::    Detecting preprocessor symbols
* Running the Compiler::        Detecting language or header features
* Running the Linker::          Detecting library features
* Runtime::                     Testing for runtime features
* Systemology::                 A zoology of operating systems
* Multiple Cases::              Tests for several possible values