exception
my $exception = exception { ... };
"exception" takes a bare block of code and returns the exception thrown by that block. If no exception
was thrown, it returns undef.
Achtung! If the block results in a false exception, such as 0 or the empty string, Test::Fatal itself
will die. Since either of these cases indicates a serious problem with the system under testing, this
behavior is considered a feature. If you must test for these conditions, you should use Try::Tiny's
try/catch mechanism. (Try::Tiny is the underlying exception handling system of Test::Fatal.)
Note that there is no TAP assert being performed. In other words, no "ok" or "not ok" line is emitted.
It's up to you to use the rest of "exception" in an existing test like "ok", "isa_ok", "is", et cetera.
Or you may wish to use the "dies_ok" and "lives_ok" wrappers, which do provide TAP output.
"exception" does not alter the stack presented to the called block, meaning that if the exception
returned has a stack trace, it will include some frames between the code calling "exception" and the
thing throwing the exception. This is considered a feature because it avoids the occasionally twitchy
"Sub::Uplevel" mechanism.
Achtung! This is not a great idea:
sub exception_like(&$;$) {
my ($code, $pattern, $name) = @_;
like( &exception($code), $pattern, $name );
}
exception_like(sub { }, qr/foo/, 'foo appears in the exception');
If the code in the "..." is going to throw a stack trace with the arguments to each subroutine in its
call stack (for example via "Carp::confess", the test name, "foo appears in the exception" will itself be
matched by the regex. Instead, write this:
like( exception { ... }, qr/foo/, 'foo appears in the exception' );
If you really want a test function that passes the test name, wrap the arguments in an array reference to
hide the literal text from a stack trace:
sub exception_like(&$) {
my ($code, $args) = @_;
my ($pattern, $name) = @$args;
like( &exception($code), $pattern, $name );
}
exception_like(sub { }, [ qr/foo/, 'foo appears in the exception' ] );
To aid in avoiding the problem where the pattern is seen in the exception because of the call stack,
$Carp::MaxArgNums is locally set to -1 when the code block is called. If you really don't want that, set
it back to whatever value you like at the beginning of the code block. Obviously, this solution doens't
affect all possible ways that args of subroutines in the call stack might taint the test. The intention
here is to prevent some false passes from people who didn't read the documentation. Your punishment for
reading it is that you must consider whether to do anything about this.
Achtung: One final bad idea:
isnt( exception { ... }, undef, "my code died!");
It's true that this tests that your code died, but you should really test that it died fortherightreason. For example, if you make an unrelated mistake in the block, like using the wrong dereference,
your test will pass even though the code to be tested isn't really run at all. If you're expecting an
inspectable exception with an identifier or class, test that. If you're expecting a string exception,
consider using "like".
success
try {
should_live;
} catch {
fail("boo, we died");
} success {
pass("hooray, we lived");
};
"success", exported only by request, is a Try::Tiny helper with semantics identical to "finally", but the
body of the block will only be run if the "try" block ran without error.
Although almost any needed exception tests can be performed with "exception", success blocks may
sometimes help organize complex testing.
dies_oklives_ok
Exported only by request, these two functions run a given block of code, and provide TAP output
indicating if it did, or did not throw an exception. These provide an easy upgrade path for replacing
existing unit tests based on "Test::Exception".
RJBS does not suggest using this except as a convenience while porting tests to use Test::Fatal's
"exception" routine.
use Test::More tests => 2;
use Test::Fatal qw(dies_ok lives_ok);
dies_ok { die "I failed" } 'code that fails';
lives_ok { return "I'm still alive" } 'code that does not fail';
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