--- /dev/null
+## Copyright (C) 2005-2012 Paul Kienzle
+##
+## This file is part of Octave.
+##
+## Octave is free software; you can redistribute it and/or modify it
+## under the terms of the GNU General Public License as published by
+## the Free Software Foundation; either version 3 of the License, or (at
+## your option) any later version.
+##
+## Octave is distributed in the hope that it will be useful, but
+## WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+## General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with Octave; see the file COPYING. If not, see
+## <http://www.gnu.org/licenses/>.
+##
+## Original version by Paul Kienzle distributed as free software in the
+## public domain.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {} fail (@var{code})
+## @deftypefnx {Function File} {} fail (@var{code}, @var{pattern})
+## @deftypefnx {Function File} {} fail (@var{code}, 'warning', @var{pattern})
+##
+## Return true if @var{code} fails with an error message matching
+## @var{pattern}, otherwise produce an error. Note that @var{code}
+## is a string and if @var{code} runs successfully, the error produced is:
+##
+## @example
+## expected error but got none
+## @end example
+##
+## If the code fails with a different error, the message produced is:
+##
+## @example
+## @group
+## expected <pattern>
+## but got <text of actual error>
+## @end group
+## @end example
+##
+## The angle brackets are not part of the output.
+##
+## Called with three arguments, the behavior is similar to
+## @code{fail(@var{code}, @var{pattern})}, but produces an error if no
+## warning is given during code execution or if the code fails.
+## @seealso{assert}
+## @end deftypefn
+
+## Author: Paul Kienzle <pkienzle@users.sf.net>
+
+function ret = fail (code, pattern, warning_pattern)
+
+ if (nargin < 1 || nargin > 3)
+ print_usage ();
+ endif
+
+ ## sort out arguments
+ test_warning = (nargin > 1 && strcmp (pattern, "warning"));
+ if (nargin == 3)
+ pattern = warning_pattern;
+ elseif (nargin == 1 || (nargin == 2 && test_warning))
+ pattern = "";
+ endif
+
+ ## match any nonempty message
+ if (isempty (pattern))
+ pattern = ".";
+ endif
+
+ ## allow assert(fail())
+ if (nargout)
+ ret = 1;
+ endif
+
+ if (test_warning)
+ ## Perform the warning test.
+ ## Clear old warnings.
+ lastwarn ();
+ ## Make sure warnings are turned on.
+ state = warning ("query", "quiet");
+ warning ("on", "quiet");
+ try
+ ## printf("lastwarn before %s: %s\n",code,lastwarn);
+ evalin ("caller", sprintf ("%s;", code));
+ ## printf("lastwarn after %s: %s\n",code,lastwarn);
+ ## Retrieve new warnings.
+ err = lastwarn ();
+ warning (state.state, "quiet");
+ if (isempty (err))
+ msg = sprintf ("expected warning <%s> but got none", pattern);
+ else
+ ## Transform "warning: ...\n" to "...".
+ err([1:9, end]) = [];
+ if (! isempty (regexp (err, pattern, "once")))
+ return;
+ endif
+ msg = sprintf ("expected warning <%s>\nbut got <%s>", pattern, err);
+ endif
+ catch
+ warning (state.state, "quiet");
+ err = lasterr;
+ ## Transform "error: ...\n", to "...".
+ err([1:7, end]) = [];
+ msg = sprintf ("expected warning <%s> but got error <%s>", pattern, err);
+ end_try_catch
+
+ else
+ ## Perform the error test.
+ try
+ evalin ("caller", sprintf ("%s;", code));
+ msg = sprintf ("expected error <%s> but got none", pattern);
+ catch
+ err = lasterr ();
+ if (strcmp (err(1:7), "error:"))
+ err([1:6, end]) = []; # transform "error: ...\n", to "..."
+ endif
+ if (! isempty (regexp (err, pattern, "once")))
+ return;
+ endif
+ msg = sprintf ("expected error <%s>\nbut got <%s>", pattern, err);
+ end_try_catch
+ endif
+
+ ## If we get here, then code didn't fail or error didn't match.
+ error (msg);
+
+endfunction
+
+
+%!fail ('[1,2]*[2,3]', 'nonconformant')
+%!fail ("fail('[1,2]*[2;3]', 'nonconformant')", "expected error <nonconformant> but got none")
+%!fail ("fail('[1,2]*[2,3]','usage:')", "expected error <usage:>\nbut got.*nonconformant")
+%!fail ("warning('test warning')", 'warning','test warning');
+
+##% !fail ("warning('next test')",'warning','next test'); ## only allowed one warning test?!?
+
+%% Test that fail() itself will generate an error
+%!error fail ("1");
+%!error <undefined> fail ('a*[2;3]', 'nonconformant')
+%!error <expected error> fail ('a*[2,3]', 'usage:')
+%!error <warning failure> fail ("warning('warning failure')", 'warning', 'success')