You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: test_constructor.m
    path of file: ./repos/chebfun/tests/chebfun2
    
    the code of the file until where you have to start completion: function pass = test_constructor( pref ) 
% This tests the chebfun2 constructor.  

if ( nargin < 1 
    
function that failed:
f = @(x,y) 1./(1+25*x.^2.*y.^2);
ffch = chebfun2(@(x,y) f(x,y), [-2 2 -2 2]);
xx = linspace(-2,2); 
[XX,YY] = meshgrid(xx,xx);
pass(7) = ( max(max( abs(f(XX,YY) - ffch(XX,YY) ))) < 2e4*tol );

% Test that #928 is fixed.
f = chebfun2(@(x,y) 1, 'vectorize');
g = chebfun2(1);
pass(8) = norm(f - g) < tol;
f = chebfun2(@(x,y) 1, 'vectorize');
g = chebfun2(1);
pass(9) = norm(f - g) < tol;

% Test that the 2nd argument can be a preference:
p = pref;
p.tech = @trigtech;
f = chebfun2(@(x,y) sin(pi*x).*cos(pi*y), p);
g = chebfun2(@(x,y) sin(pi*x).*cos(pi*y), [-1 1 -1 1], p);
pass(10) = norm(f - g) < tol;

% Test the length of chebfun2s in different directions:
p.tech = @chebtech2;
f = chebfun2(@(x,y) sin(80*x+y), p);
pass(11) = length(f.cols(:,1)) < 50;

% Test whether there is a huge overesimation in the length of chebfun2s:
f = chebfun(@(x) 1./(1+25*x.^2));
f2 = chebfun2(@(x,y) 1./(1+25*x.^2));
pass(12) = length(f2.rows) < length(f)+20;

% Test whether reconstructing rows gives the same length.
f = chebfun2(@(x,y) cos(pi*x.*y));
frows = chebfun(f.rows);
pass(13) = abs(length(frows)-length(f.rows)) < 10;

end