Today we look at captains whose tenure included:
Only wins
Only losses
Only draws.
Only wins (complete list):

16 instances here. Bacher and Lord Hawke had the best stretches of 4 wins out of 4. In the former case all 4 wins came in a single series against Australia. In the latter case they were part of 5 wins out of 5 in his Test career, although he was a specialist (?) batsman with a single-figure batting average.
Those with 2 wins out of 2 are mainly stand-ins (Rahane and Jacobs) in recent times. Similarly for those who won their only Tests as captain (eg Shastri, Harvey, WA Brown).
Rahane is the most recent player here.
Only losses (2 or more):

Headed by the Bangladeshi duo of Khaled Mashud (12) and Khaled Mahmud (9) in their team’s early years.
However, there is also KC Brathwaite (5) from WI in recent years along with Porterfield who has led Ireland in all 3 of its Tests. DK Gaekwad, now India’s oldest living player, has 4 losses. (In that series Pankaj Roy captained for 1 Test, which was also lost).
Some other well-known players found here are AJ Lamb, AR Morris, JE Emburey and RS Madugalle.
And FL Reifer, captaining the WI third XI against Bangladesh at home. When he talked of winning the series, local journalists asked “Are you smoking something # which sounds like your name?”
# Reefer, a term for marijuana or ganja
Only draws (complete list):

The list of 21 is headed by Srikkanth (all 4 in a single series against Pakistan in Pakistan). Majid and Saeed also drew all 3 Tests in a single series.
There is no one here since BA Murphy (1 Test in 2001). Well-known players not mentioned so far include DL Murray, G Kirsten, GA Headley, MA Butcher, RR Lindwall and TW Graveney. Practically all of the 1 or 2-Test captains were stand-ins.
Srikkanth and Adhikari are the only ones from India. This did not help Srikkanth much as he was promptly replaced by Azharuddin. And Adhikari stopped a sequence of 3 heavy losses with a draw where his team narrowly escaped defeat.