Experiment with Hypothesis(https://hypothesis.readthedocs.org/en/master/index.html) and testing WEB2PY (http://web2py.com). These tests are only for a few web2py validators.

test_validators.py

from decimal import Decimal
import json
import unittest

from hypothesis import given, strategies as st

from gluon import validators as vld


# JSON Test related code: http://jerith.github.io/pyconza2015-property-based-testing-with-Hypothesis/#/4/3
def nest_data(st_values):
    return st.lists(st_values) | st.dictionaries(st.text(), st_values)


def nested_data():
    return st.none() | st.integers() | st.floats(-1e308, 1e308) | st.text()


class TestValidators(unittest.TestCase):

    @given(st.text())
    def test_IS_ALPHANUMERIC(self, value):
        result = vld.IS_ALPHANUMERIC()(value)
        assert (result == (value, None)) or (result == (value, 'Enter only letters, numbers, and underscore'))

    @given(maxsize=st.integers(), minsize=st.integers(), value=st.text())
    def test_IS_LENGTH(self, maxsize, minsize, value):
        result = vld.IS_LENGTH(maxsize=maxsize, minsize=minsize)(value)
        assert (result == (value, None)) or (result == (value, 'Enter from %s to %s characters' % (minsize, maxsize)))

    @given(maxsize=st.integers(), minsize=st.integers(), value=st.floats(), dot=st.characters())
    def test_IS_DECIMAL_IN_RANGE(self, maxsize, minsize, value, dot):
        result = vld.IS_DECIMAL_IN_RANGE(maximum=maxsize, minimum=minsize, dot=dot)(value)
        assert (result == (Decimal(value), None)) or (result == (Decimal(value), 'Enter from %s to %s characters' % (minsize, maxsize)))

    @given(
        theset=st.lists(st.text()),
        labels=st.none() | st.lists(st.text()),
        error_message=st.just('Value not allowed'),
        multiple=st.booleans(),
        zero=st.just(''),
        sort=st.booleans(),
        value=st.text()
    )
    def test_IS_IN_SET(self, theset, labels, error_message, multiple, zero, sort, value):
        result = vld.IS_IN_SET(theset, labels, error_message, multiple, zero, sort)(value)
        assert (result == (value, None)) or (result == (value, 'Value not allowed'))

    @given(
        data=st.recursive(nested_data(), nest_data) | st.text(),
        native_json=st.booleans(),
        error_message=st.just('Invalid json')
    )
    def test_IS_JSON(self, data, native_json, error_message):
        result = vld.IS_JSON(error_message=error_message, native_json=native_json)(json.dumps(data))
        js = json.dumps(data) if native_json else data
        assert result == (js, None) or result == (js, 'Invalid json')


if __name__ == '__main__':
    unittest.main()

zresults

Finding files... done.
Importing test modules ... done.

Falsifying example: test_IS_DECIMAL_IN_RANGE(self=<test_validators.TestValidators testMethod=test_IS_DECIMAL_IN_RANGE>, maxsize=0, minsize=0, value=0.0, dot=u'0')
Falsifying example: test_IS_IN_SET(self=<test_validators.TestValidators testMethod=test_IS_IN_SET>, theset=[], labels=None, error_message='Value not allowed', multiple=True, zero='', sort=False, value=u'')
Falsifying example: test_IS_LENGTH(self=<test_validators.TestValidators testMethod=test_IS_LENGTH>, maxsize=1000000, minsize=1, value=u'')
======================================================================
FAIL: test_IS_DECIMAL_IN_RANGE (test_validators.TestValidators)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "D:\code\git\web2py_hypothesis\tests\test_validators.py", line 32, in test_IS_DECIMAL_IN_RANGE
    def test_IS_DECIMAL_IN_RANGE(self, maxsize, minsize, value, dot):
  File "D:\programs\open\python27\lib\site-packages\hypothesis\core.py", line 540, in wrapped_test
    print_example=True, is_final=True
  File "D:\programs\open\python27\lib\site-packages\hypothesis\executors.py", line 57, in default_new_style_executor
    return function(data)
  File "D:\programs\open\python27\lib\site-packages\hypothesis\core.py", line 103, in run
    return test(*args, **kwargs)
  File "D:\code\git\web2py_hypothesis\tests\test_validators.py", line 34, in test_IS_DECIMAL_IN_RANGE
    assert (result == (Decimal(value), None)) or (result == (Decimal(value), 'Enter from %s to %s characters' % (minsize, maxsize)))
AssertionError

======================================================================
FAIL: test_IS_IN_SET (test_validators.TestValidators)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "D:\code\git\web2py_hypothesis\tests\test_validators.py", line 37, in test_IS_IN_SET
    theset=st.lists(st.text()),
  File "D:\programs\open\python27\lib\site-packages\hypothesis\core.py", line 540, in wrapped_test
    print_example=True, is_final=True
  File "D:\programs\open\python27\lib\site-packages\hypothesis\executors.py", line 57, in default_new_style_executor
    return function(data)
  File "D:\programs\open\python27\lib\site-packages\hypothesis\core.py", line 103, in run
    return test(*args, **kwargs)
  File "D:\code\git\web2py_hypothesis\tests\test_validators.py", line 47, in test_IS_IN_SET
    assert (result == (value, None)) or (result == (value, 'Value not allowed'))
AssertionError

======================================================================
FAIL: test_IS_LENGTH (test_validators.TestValidators)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "D:\code\git\web2py_hypothesis\tests\test_validators.py", line 27, in test_IS_LENGTH
    def test_IS_LENGTH(self, maxsize, minsize, value):
  File "D:\programs\open\python27\lib\site-packages\hypothesis\core.py", line 540, in wrapped_test
    print_example=True, is_final=True
  File "D:\programs\open\python27\lib\site-packages\hypothesis\executors.py", line 57, in default_new_style_executor
    return function(data)
  File "D:\programs\open\python27\lib\site-packages\hypothesis\core.py", line 103, in run
    return test(*args, **kwargs)
  File "D:\code\git\web2py_hypothesis\tests\test_validators.py", line 29, in test_IS_LENGTH
    assert (result == (value, None)) or (result == (value, 'Enter from %s to %s characters' % (minsize, maxsize)))
AssertionError

----------------------------------------------------------------------
Ran 5 tests in 4.252s

FAILED (failures=3)