This is not "better than TAP" but rather better than implementing tests as captures of psql outputs as done in pg_regress. Besides that, there are other feature

This is not "better than TAP" but rather better than implementing tests as captures of psql outputs as done in pg_regress. Besides that, there are other features that are harder or impossible to test in pg_regress, like binary encodings of types. Plus, it provides TAP output for test runners/printers that support it.