In the gcc.c-torture test suites, test cases are commonly named
after the date on which they were added. This allows people to tell
at a glance whether a test failure is because of a recently found bug
that has not yet been fixed, or whether it may be a regression. In
other test suites, more descriptive names are used. In general C test
cases have a trailing -n.c, starting with -1.c, in
case other test cases with similar names are added later.
Test cases should use abort () to indicate failure and
exit (0) for success; on some targets these may be redefined to
indicate failure and success in other ways.
In the gcc.dg test suite, it is often necessary to test that an
error is indeed a hard error and not just a warning--for example,
where it is a constraint violation in the C standard, which must
become an error with -pedantic-errors. The following idiom,
where the first line shown is line line of the file and the line
that generates the error, is used for this:
/* { dg-bogus "warning" "warning in place of error" } */
/* { dg-error "regexp" "message" { target *-*-* } line } */
It may be necessary to check that an expression is an integer constant
expression and has a certain value. To check that E has
value V, an idiom similar to the following is used:
char x[((E) == (V) ? 1 : -1)];
In gcc.dg tests, __typeof__ is sometimes used to make
assertions about the types of expressions. See, for example,
gcc.dg/c99-condexpr-1.c. The more subtle uses depend on the
exact rules for the types of conditional expressions in the C
standard; see, for example, gcc.dg/c99-intconst-1.c.
It is useful to be able to test that optimizations are being made
properly. This cannot be done in all cases, but it can be done where
the optimization will lead to code being optimized away (for example,
where flow analysis or alias analysis should show that certain code
cannot be called) or to functions not being called because they have
been expanded as built-in functions. Such tests go in
gcc.c-torture/execute. Where code should be optimized away, a
call to a nonexistent function such as link_failure () may be
inserted; a definition
#ifndef __OPTIMIZE__
void
link_failure (void)
{
abort ();
}
#endif
will also be needed so that linking still succeeds when the test is
run without optimization. When all calls to a built-in function
should have been optimized and no calls to the non-built-in version of
the function should remain, that function may be defined as
static to call abort () (although redeclaring a function
as static may not work on all targets).
All testcases must be portable. Target-specific testcases must have appropriate code to avoid causing failures on unsupported systems; unfortunately, the mechanisms for this differ by directory.
FIXME: discuss non-C test suites here.