function testerror(fn, id, msg)
%TESTERROR check that a function throws an expected error
%
%     testerror(fn[, id[, msg]])
%     testerror(@() statement[, id[, msg]])
%
% Test that a function, possibly created on the fly for a bad statement, throws
% an error. Optionally check that the error string is the one expected.
%
% OK or FAILURE is verbosely reported. This is for use in test cases.
%
% Inputs:
%       fn @fn handle to test function (should take no arguments)
%       id str OPTIONAL: expected error id string (empty or missing to bypass check)
%      msg str OPTIONAL: expected error message string

% Iain Murray, September 2010

try
    fn();
%catch me
catch
    % Instead of the 'catch me' line, do a plain catch with the (deprecated)
    % following line for compatability with older Matlab/Octave
    [me.message, me.identifier] = lasterr;
    if (nargin > 1) && ~isempty(id)
        if ~isequal(me.identifier, id)
            fprintf('FAILURE: unexpected error identifier: %s\n', me.identifier);
            return;
        end
    end
    if (nargin > 2) && ~isempty(msg)
        if ~isequal(me.message, msg)
            fprintf('FAILURE: unexpected error message: %s\n', me.message);
            return;
        end
    end
    fprintf('OK          (error was thrown as expected)\n');
    return;
end

fprintf('FAILURE: no error thrown when one was expected\n');