A = tridiagonal(0, -1, 2, -1);
expected = [];
unit_test_equals("poisson tridiagonal of size zero is correct", ...
		 expected, ...
		 A);

A = tridiagonal(1, -1, 2, -1);
expected = [2];
unit_test_equals("poisson tridiagonal of size one is correct", ...
		 expected, ...
		 A);

A = tridiagonal(2, -1, 2, -1);
expected = [2, -1; ...
	    -1, 2];
unit_test_equals("poisson tridiagonal of size two is correct", ...
		 expected, ...
		 A);

A = tridiagonal(3, -1, 2, -1);
expected = [2, -1, 0; ...
	    -1, 2, -1;
	    0, -1, 2];
unit_test_equals("poisson tridiagonal of size three is correct", ...
		 expected, ...
		 A);
