Unit testing in PostgreSQL with pgTap

The applications I work with use procedural functions and RDBMS features quite heavily, and although we have unit tests for application code, we currently have no unit testing directly in the database. I’ll be the first to admit that I can be fairly highly strung when making large changes to our systems, and having a suite of unit tests to run is a great way to extinguish any histrionics.

I’ve been looking at pgTap today which provides an excellent way to perform unit testing in PostgreSQL covering pretty much every aspect of the schema.

To install pgTap we just download, make and install just like any other extension:

$ cd /usr/pgsql_src
$ wget http://api.pgxn.org/dist/pgtap/0.94.0/pgtap-0.94.0.zip
$ unzip pgtap-0.94.0.zip && cd pgtap*
$ make
$ make installcheck PGUSER=glyn
$ sudo make install

The system I’m testing on is still running Postgres 9.0, so to install the extension I have to revert to running the sql script rather than “CREATE EXTENSION”, and for some reason the pgtap.sql script didn’t end up in my contrib directory along with the sql for the extension based versions, so I just copied it there manually before running it:

$ cp sql/pgtap.sql `pg_config --sharedir`/contrib
$ psql -d TEST -f `pg_config --sharedir`/contrib/pgtap.sql 

If this were 9.1+ that would just be just be:

$ psql -d TEST -c "CREATE EXTENSION pgtap"

Now pgTap is installed I can run a test that checks nothing. We perform all tests within a transaction which is rolled back at the end to ensure our tests do not make any persistent changes.

TEST=# BEGIN;
BEGIN
TEST=# SELECT plan(1);
 plan
------
 1..1
(1 row)
TEST=# SELECT pass( 'Testing nothing' );
	  pass
------------------------
 ok 1 - Testing nothing
(1 row)
TEST=# SELECT * FROM finish();
 finish
--------
(0 rows)
TEST=# ROLLBACK;
ROLLBACK

The output basically means; 1..1 we ran 1 of 1 tests and ok 1 – Testing nothing test number 1, with description “Testing nothing” returned “ok”. The above looks a bit messy and the docs recommend setting the following in psql to make the behaviour and output a little easier to handle:

\set ECHO
\set QUIET 1
\pset format unaligned
\pset tuples_only true
\pset pager
\set ON_ERROR_ROLLBACK 1
\set ON_ERROR_STOP true
\set QUIET 1

Now lets create a function and perform an actual test on the results:

TEST=# CREATE OR REPLACE FUNCTION public.test1(text) RETURNS text AS 'SELECT upper($1) || length($1)::text' language 'SQL';

TEST=# BEGIN;
TEST=# SELECT plan(1);
1..1
TEST=# SELECT results_eq(E'SELECT * FROM public.test1(\'glyn\')', E'SELECT upper(\'glyn\') || length(\'glyn\')::text','public.test1() should return text in uppercase suffixed with length');
ok 1 - public.test1() should return text in uppercase suffixed with length
TEST=# SELECT * FROM finish();
TEST=# ROLLBACK;

We can also simply test if some operation like an insert succeeds:

TEST=# CREATE TABLE public.table1 (a text, b integer);
	
TEST=# BEGIN;
TEST=# SELECT plan(1);
1..1
TEST=# SELECT lives_ok(E'INSERT INTO public.table1 VALUES (\'TEST\', 1)');
ok 1
TEST=# SELECT * FROM finish();
TEST=# ROLLBACK;

…and we can check that performing some operation fails with a particular exception:

TEST=# BEGIN;
TEST=# SELECT plan(1);
1..1
TEST=# SELECT throws_ok(E'INSERT INTO public.table1 VALUES (\'test\', \'not an integer\')','22P02',NULL,'Column b is an integer, inserting text should fail');
ok 1 - Column b is an integer, inserting text should fail
TEST=# SELECT * FROM finish();
TEST=# ROLLBACK;	

We can test if an operation created the expected data too, if I create a trigger on my test table to uppercase any text inserted, we can check if it worked as expected:

TEST=# CREATE FUNCTION public.table1_upper_func() RETURNS trigger AS $$ BEGIN NEW.a := upper(NEW.a); RETURN NEW; END; $$ LANGUAGE plpgsql VOLATILE;
TEST=# CREATE TRIGGER table1_upper_trig BEFORE INSERT OR UPDATE ON public.table1 FOR EACH ROW EXECUTE PROCEDURE public.table1_upper_func();
	
TEST=# BEGIN;
TEST=# SELECT plan(1);
1..1
TEST=# INSERT INTO public.table1 VALUES ('test',1);
TEST=# SELECT is(a, 'TEST', 'Inserted values into column "a" should be uppercased' ) FROM public.table1 WHERE b = 1;
ok 1 - Inserted values into column "a" should be uppercased
TEST=# SELECT * FROM finish();
TEST=# ROLLBACK;

We can also test the existence and structure of a table:

TEST=# CREATE INDEX ON public.table1 USING btree(b);
TEST=#
TEST=# BEGIN;
TEST=# SELECT plan(6);
1..6
TEST=# SELECT has_table('public', 'table1', 'table public.table1 exists' );
ok 1 - table public.table1 exists
TEST=# SELECT has_column('public', 'table1', 'a', 'column public.table1.a exists');
ok 2 - column public.table1.a exists
TEST=# SELECT col_type_is('public', 'table1', 'a', 'text', 'Type of column public.table1.a is text');
ok 3 - Type of column public.table1.a is text
TEST=# SELECT has_column('public', 'table1', 'b', 'column public.table1.b exists');
ok 4 - column public.table1.b exists
TEST=# SELECT col_type_is('public', 'table1', 'b', 'integer', 'Type of column public.table1.b is integer');
ok 5 - Type of column public.table1.b is integer
TEST=# SELECT has_index('public', 'table1','table1_b_idx', 'Table public.table1 has an index table1_b_idx');
ok 6 - Table public.table1 has an index table1_b_idx
TEST=# SELECT * FROM finish();
TEST=# ROLLBACK;

To wrap all of this up pgTap provides a runtests() function that will run predefined test functions without us having to define the number of tests with plan(n) or run finish(), and we can write these functions just like any other function incorporating the tests demonstrated above. By default the function looks for function names starting with test, it’s probably a good idea to put the tests in a specific schema or give them a more unique name than that.

When runtests() is run it also first looks for functions starting with “startup” or “shutdown” and these are run in alphabetical order before and after a whole set of test functions respectively. In addition functions starting with “setup” or “teardown” are, again, run in alphabetical order before and after each test function respectively. Typically these would be used to check, perform and undo any data changes required by each and or all tests, for example if we’ve called a sequence that doesn’t belong to a table during our tests, it’s value won’t be rolled back so we might want to reset it’s value.

One thing to clarify though (which came to my attention when running pg_prove blelow), is that where the “setup” and “teardown” functions are automatically rolled back at the end of each test, the “startup” and “shutdown” functions are not automatically rolled back at the end of the tests. If you want that functionality then you need to wrap your call to runtests in a transaction and roll it back at the end just as before.

E.g. we can create our test schema and functions:

CREATE SCHEMA unit_testing;

TEST=# CREATE OR REPLACE FUNCTION unit_testing.setup_tap_test_example() 
RETURNS SETOF TEXT AS $$
BEGIN
	INSERT INTO public.table1 VALUES ('test',1);
	RETURN NEXT is(a, 'TEST', 'Should have initial row in table1') FROM public.table1 WHERE b = 1;
END;
$$ LANGUAGE plpgsql;

TEST=# CREATE OR REPLACE FUNCTION unit_testing.tap_test_example() 
RETURNS SETOF TEXT AS $$
BEGIN
	RETURN NEXT has_table('public', 'table1', 'table public.table1 exists' );
	RETURN NEXT has_column('public', 'table1', 'a', 'column public.table1.a exists');
	RETURN NEXT col_type_is('public', 'table1', 'a', 'text', 'Type of column public.table1.a is text');
	RETURN NEXT has_column('public', 'table1', 'b', 'column public.table1.b exists');
	RETURN NEXT col_type_is('public', 'table1', 'b', 'integer', 'Type of column public.table1.b is integer');
	RETURN NEXT has_index('public', 'table1','table1_b_idx', 'Table public.table1 has an index table1_b_idx');
END;
$$ LANGUAGE plpgsql;

TEST=# CREATE OR REPLACE FUNCTION unit_testing.teardown_tap_test_example() 
RETURNS SETOF TEXT AS $$
BEGIN
	RETURN NEXT lives_ok('DELETE FROM public.table1 WHERE b = 1');
END;
$$ LANGUAGE plpgsql;

Now we can run them:

TEST=# BEGIN;
TEST=# SELECT * FROM runtests('unit_testing','^tap_test_example');
ok 1 - Should have initial row in table1
# unit_testing.tap_test_example()
ok 2 - table public.table1 exists
ok 3 - column public.table1.a exists
ok 4 - Type of column public.table1.a is text
ok 5 - column public.table1.b exists
ok 6 - Type of column public.table1.b is integer
ok 7 - Table public.table1 has an index table1_b_idx
ok 8
1..8
TEST=# ROLLBACK;

Gravy. We can, if we want, also install the pg_prove module from cpan to finish wrapping it all together with TAP::Harness and provide a summary of our tests:

$ sudo cpan TAP::Parser::SourceHandler::pgTAP
$ pg_prove -d TEST -R -s unit_testing -x '^tap_test_example'
runtests('unit_testing'::name, '^tap_test_example'::text); ..
# unit_testing.tap_test_example()
runtests('unit_testing'::name, '^tap_test_example'::text); .. ok
All tests successful.
Files=1, Tests=9,  0 wallclock secs ( 0.05 usr  0.02 sys +  0.00 cusr  0.01 csys =  0.08 CPU)
Result: PASS

This is just a small example of some of the tests we can do with pgTap, the suite provides a very extensive set of tests. See the documentation here.

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