BEGIN;
CREATE SCHEMA doctest;
CREATE EXTENSION pgtap;
CREATE EXTENSION pg_doctest WITH SCHEMA doctest;
CREATE SCHEMA foo;
CREATE OR REPLACE FUNCTION foo.add ( a INT, b INT)
RETURNS INT LANGUAGE SQL
AS $$
    -- >>> SELECT foo.add(1,1)
    -- 2
    -- >>> SELECT foo.add(NULL,9)
    -- NULL
    -- >>> SELECT foo.add(4,2)
    -- 42
    SELECT a+b;
$$;
SELECT runtests('doctest'::NAME);
                  runtests                   
---------------------------------------------
     # Subtest: doctest.test()
     # doctests for foo.add(integer,integer)
     ok 1 - SELECT foo.add(1,1)
     ok 2 - SELECT foo.add(NULL,9)
     not ok 3 - SELECT foo.add(4,2)         +
     # Failed test 3: "SELECT foo.add(4,2)" +
     #         have: 6                      +
     #         want: 42
     1..3
     # Looks like you failed 1 tests of 3
 not ok 1 - doctest.test                    +
 # Failed test 1: "doctest.test"
 1..1
 # Looks like you failed 1 test of 1
(10 rows)

ROLLBACK;