How to test PROCEDURE in PostgreSQL with pgTAP?

Question

Is there a best practice for unit testing a PostgreSQL 11+ PROCEDURE (NOT a FUNCTION) using pgTap.

For example, how would one recommend unit testing a stored procedure like this:

CREATE OR REPLACE PROCEDURE foo.do_something(IN i_value INT)
AS
$$
BEGIN
  PERFORM foo.call_function_1(i_value);
  COMMIT;      
  PERFORM foo.call_function_2(i_value);
  COMMIT;      
  CALL foo.another_procedure(i_value);
END;
$$
LANGUAGE plpgsql;

This becomes difficult since pgTap unit tests run via a stored function like this:

SELECT * FROM runtests('foo'::NAME);

This executes in a transaction, making it impossible to execute stored procedures that modify transaction state by calling COMMIT or ROLLBACK.

Answer 1

Here is an approach I came up with inspired by using interfaces along with mocking frameworks in other languages.

First we move the COMMIT operation to a stored procedure like this:

CREATE PROCEDURE foo.do_commit()
AS
$$
BEGIN
  COMMIT;
END;
$$
LANGUAGE plpgsql;

Then we alter the actual stored procedure to call do_commit instead of using COMMIT command directly. For example:

CREATE OR REPLACE PROCEDURE foo.do_something(IN i_value INT)
AS
$$
BEGIN
  PERFORM foo.call_function_1(i_value);
  CALL foo.do_commit();
  CALL foo.another_procedure(i_value);
END;
$$
LANGUAGE plpgsql;

Since the unit tests are executed in a transaction that gets rolled back, we can replace the do_commit call temporarily to something mocked out for testing. A test could look something like this:

CREATE FUNCTION test.test_do_something()
RETURNS SETOF TEXT 
AS 
$$
BEGIN
  CREATE TEMPORARY TABLE commit_calls
  (
    commit_call BOOLEAN NOT NULL DEFAULT TRUE
  )
  ON COMMIT DROP;

  CREATE TEMPORARY TABLE function_calls
  (
    the_value INT NOT NULL
  )
  ON COMMIT DROP;

  CREATE OR REPLACE PROCEDURE foo.do_commit()
  AS
  $mock_do_commit$
  BEGIN
    INSERT INTO commit_calls (commit_call)
    VALUES (DEFAULT);
  END;
  $mock_do_commit$
  LANGUAGE plpgsql;

  CREATE OR REPLACE FUNCTION foo.call_function_1(i_value INT)
  RETURNS VOID
  AS
  $mock_call_function_1$
    INSERT INTO function_calls (the_value)
    VALUES (i_value);
  $mock_call_function_1$
  LANGUAGE sql;

  -- EXECUTE
  CALL foo.do_something(9);
  CALL foo.do_something(100);

  -- VERIFY
  RETURN NEXT assert.is((SELECT COUNT(*) FROM commit_calls)::INT, 2, 'verify transaction commits');
  RETURN NEXT assert.bag_eq(
    'SELECT the_value FROM function_calls',
    'VALUES (9), (100)',
    'verify function call values');
END;
$$
LANGUAGE plpgsql;

The idea is to temporarily mock out actual function calls for testing.
This way one can unit test a stored procedure without committing real transactions.
When the test ends it rolls back the transaction and the all of the changes are discarded.