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 for the right reason. 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_ok

lives_ok

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';