India has been on a long streak of test series where it has managed at least one win. I am counting two-match series but not one-off tests. With the Durban win, India now extends that streak to 19 easily the highest among the teams currently playing.
Australia has 23 consecutive series between 2002 and 2008.
Not surprisingly the West Indies beats them with 33 consecutive series between 1980 and 1997 and I would be surprised if any other team has done better.
What's the longest such streak for other countries?