A problem I'm encountering with pgTAP (http://pgtap.org/)

output.txt

$ foreman start -f Procfile.test
19:33:03 pg.1   | started with pid 84863
19:33:03 test.1 | started with pid 84864
19:33:03 pg.1   | LOG:  database system was shut down at 2015-08-02 19:23:13 EDT
19:33:03 pg.1   | LOG:  MultiXact member wraparound protections are now enabled
19:33:03 pg.1   | LOG:  database system is ready to accept connections
19:33:03 pg.1   | LOG:  autovacuum launcher started
19:33:04 test.1 | ok 1 - Function VALIDATE_SPECIFICATION(JSONB, JSONB) should exist
19:33:04 test.1 | ok 2 - Valid objects are validated
19:33:04 pg.1   | WARNING:  Missing required key "oops"
19:33:04 test.1 | ok 3 - Invalid objects are rejected
19:33:04 pg.1   | WARNING:  Missing required key "oops"
19:33:04 pg.1   | CONTEXT:  SQL statement "
19:33:04 pg.1   |               SELECT public.VALIDATE_SPECIFICATION(
19:33:04 pg.1   |                   '{"example": "correct"}',
19:33:04 pg.1   |                   '[
19:33:04 pg.1   |                       {"key": "example", "type": "string", "required": true},
19:33:04 pg.1   |                       {"key": "oops",    "type": "number", "required": true}
19:33:04 pg.1   |                   ]'
19:33:04 pg.1   |               );
19:33:04 pg.1   |           "
19:33:04 pg.1   |       PL/pgSQL function throws_ok(text,character,text,text) line 16 at EXECUTE statement
19:33:04 test.1 | not ok 4 - Throws useful error messages on objects with missing keys
19:33:04 test.1 | # Failed test 4: "Throws useful error messages on objects with missing keys"
19:33:04 test.1 | #       caught: no exception
19:33:04 test.1 | #       wanted: 42804
19:33:04 test.1 | # Looks like you failed 1 test of 4
19:33:05 test.1 | exited with code 0
19:33:05 system | sending SIGTERM to all processes
19:33:05 pg.1   | LOG:  received smart shutdown request
19:33:05 pg.1   | LOG:  autovacuum launcher shutting down
19:33:05 pg.1   | LOG:  shutting down
19:33:05 pg.1   | LOG:  database system is shut down
19:33:05 pg.1   | exited with code 0

tap.sql

\i test/etc/pgtap_setup.sql
SET client_min_messages = ERROR;

SELECT plan(4);

/**
 * Validate the presence of the function
 *
 * If this fails, the function was not created at all. Note that the datatypes
 * as well as the function name are all specified as lower-case in the actual
 * test itself; this is required for proper quoting per the SQL spec.
 */
SELECT has_function(
    'public', 'validate_specification', ARRAY['jsonb', 'jsonb'],
    'Function VALIDATE_SPECIFICATION(JSONB, JSONB) should exist'
);

/**
 * Validate that correct object specifications work
 *
 * This is a general usage test, but also doubles as a way to check that keys
 * specified as optional are, in fact, optional.
 */
SELECT is(
    public.VALIDATE_SPECIFICATION(
        '{"example": "correct"}',
        '[
            {"key": "example",  "type": "string", "required": true},
            {"key": "optional", "type": "number", "required": false}
        ]'
    ),
    TRUE,
    'Valid objects are validated'
);

/**
 * Validate that required keys are required
 *
 * In this test, a required key was described in the specification, but not
 * given in the object to be validated, so it should fail.
 */
SELECT is(
    public.VALIDATE_SPECIFICATION(
        '{"example": "correct"}',
        '[
            {"key": "example", "type": "string", "required": true},
            {"key": "oops",    "type": "number", "required": true}
        ]'
    ),
    FALSE,
    'Invalid objects are rejected'
);

/**
 * Validate error messages given off by missing keys
 *
 * The validation test above should guarantee that invalid objects with
 * missing keys are rejected. This test should validate that it emits a proper
 * warning message which indicates why this is the case.
 */
SELECT throws_ok(
    $ERR$
        SELECT public.VALIDATE_SPECIFICATION(
            '{"example": "correct"}',
            '[
                {"key": "example", "type": "string", "required": true},
                {"key": "oops",    "type": "number", "required": true}
            ]'
        );
    $ERR$,
    '42804',
    'Missing required key "oops"',
    'Throws useful error messages on objects with missing keys'
);

\i test/etc/pgtap_teardown.sql

validate_specification.sql

CREATE OR REPLACE
FUNCTION VALIDATE_SPECIFICATION(JSONB, JSONB)
RETURNS BOOLEAN
LANGUAGE PLPGSQL
AS $PGSQL$
DECLARE
    -- extra keys (first use), required keys (second use)
    keys TEXT[];

    -- iteration variable for checking each existing field
    spec RECORD;

    -- the return state, i.e., whether the object passes the specification
    ret BOOLEAN := TRUE;
BEGIN
    -- find any keys which are not covered by the spec
    SELECT ARRAY_AGG(jsonb_object_keys) INTO keys
    FROM
        JSONB_OBJECT_KEYS($1) LEFT JOIN
        JSONB_TO_RECORDSET($2) AS ("key" TEXT, t TEXT, r BOOLEAN) ON
        jsonb_object_keys = jsonb_to_recordset.key
    WHERE jsonb_to_recordset.key IS NULL;

    -- if we got any keys from the last query, then we've got extra keys
    IF ARRAY_LENGTH(keys, 1) > 0 THEN
        RAISE WARNING 'Extra key(s): %', ARRAY_TO_STRING(keys, ', ')
        USING ERRCODE = 'datatype_mismatch';

        -- this is a failure condition
        ret := FALSE;
    END IF;

    -- collect object keys for quick reference, reusing the 'keys' var
    SELECT ARRAY_AGG(jsonb_object_keys) INTO keys
    FROM JSONB_OBJECT_KEYS($1);

    -- iterate over the specification entries
    FOR spec IN
    SELECT *
    FROM JSONB_TO_RECORDSET($2) AS ("key" TEXT, "type" TEXT, required BOOLEAN)
    LOOP
        -- if the key declared by the spec is not contained in the object
        IF NOT (ARRAY[spec.key] <@ keys) THEN
            -- it's no big deal if the spec says it's not required
            CONTINUE WHEN NOT spec.required;

            -- otherwise make sure to tell the user why this will fail
            RAISE WARNING 'Missing required key "%"', spec.key
            USING ERRCODE = 'datatype_mismatch';

            -- and make sure we'll return that failure state
            ret := FALSE;
        END IF;

        -- check to make sure the JSON type of the given entry is correct
        IF JSONB_TYPEOF($1 #> ARRAY[spec.key]) <> spec.type THEN
            RAISE WARNING
                'Bad value ("%" is type `%`) for key "%"',
                $1 #>> ARRAY[spec.key],
                JSONB_TYPEOF($1 #> ARRAY[spec.key]),
                spec.key
            USING
                ERRCODE = 'datatype_mismatch',
                HINT    = 'The proper datatype is `' || spec.type || '`';

            -- mismatched types are a failure condition
            ret := FALSE;
        END IF;
    END LOOP;

    -- give the calling function our final state
    RETURN ret;
END;
$PGSQL$;

COMMENT ON FUNCTION VALIDATE_SPECIFICATION(JSONB, JSONB) IS $MARKDOWN$
Generic JSONB Structure Validation
==================================

The first argument to this function is the JSONB element to be validated. The
second argument is the structure used to validate it, as a JSONB array of
objects. Though the second argument is not validated (to make it possible to
send in extended objects), if each object does not have a minimum of the
following keys, the behavior is undocumented (but the function will likely
blow up):

  * `key` - A field name that should be present in the function. It must be a
    string.
  * `type` - A valid JSONB subtype. See the [docs][] for `jsonb_typeof()` for
    valid candidate values for this field.
  * `required` - A boolean value indicating whether or not the `key` **must**
    be present in the object being validated. If it is false, the `key` is
    optional.

Note that, though some fields are *required*, any fields that are not listed
**must** be *absent*, or else a warning will be raised and the object will be
considered not to match.

Diagnostics
-----------

  * 'Extra keys: x, y, ...' - When a given specification row does not describe
    all of the elements in the object being validated.
  * 'Missing required key "x"' - When a given specification row has `required`
    set to `true`, but the object being validated does not contain that key.
  * 'Bad value ("x" is type y) for key "z"' - When a given object doesn't
    match the appropriate target datatype for a given key.
    - The 'HINT' value will clarify the requested type.

Examples
--------

### Valid object:

    SELECT VALIDATE_SPECIFICATION(
        '{"example": "correct"}',
        '[
            {"key": "example",  "type": "string", "required": true}
            {"key": "optional", "type": "number", "required": false}
        ]'
    );

    => 't'

### Invalid object, missing required key "oops":

    SELECT VALIDATE_SPECIFICATION(
        '{"example": "incorrect"}',
        '[
            {"key": "example", "type": "string", "required": true},
            {"key": "oops",    "type": "string", "required": true}
        ]'
    );

    WARNING: Missing required key "oops"
    => 'f'

### Invalid object, extra keys "oops" and "bad":

    SELECT VALIDATE_SPECIFICATION(
        '{"example": "incorrect", "oops": 1, "bad": true}',
        '[{"key": "example", "type": "string", "required": true}]'
    );

    WARNING: Extra key(s): oops, bad
    => 'f'

### Invalid object, bad datatype on "bad" key:

    SELECT VALIDATE_SPECIFICATION(
        '{"example": "incorrect", "bad": "fifty"}',
        '[
            {"key": "example", "type": "string", "required": true},
            {"key": "bad",     "type": "number", "required": true},
        ]'
    );

    WARNING: Bad value ("fifty" is type `string`) for key "bad"
    HINT: The proper datatype is `number`
    => 'f'

-----

docs: http://www.postgresql.org/docs/9.4/static/functions-json.html#FUNCTIONS-JSON-PROCESSING-TABLE
$MARKDOWN$;