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 (see Language Choice). They do not cache the results of
their tests for future use (see 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
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.
See Writing Autoconf Macros, for how to do that.