Quick Start

The quickest way to start is to run klara on a python file containing a python function that is annotated with type hints. E.g. we have a file called foo.py:

def foo(x: int, y: int, z: str):
    if x + y > 2:
        return x + y + 12
    elif x < y:
        return x + y
    elif (z + "me") == "some":
        return z + "thing"
    else:
        return x - y

We can invoke klara on that file by:

klara foo.py

And it will generate a test file test_foo.py in the same directory, filled with the various test inputs:

import contract_test


def test_foo_0():
    assert contract_test.foo(0, 3, \'\') == 15
    assert contract_test.foo(0, 1, \'\') == 1
    assert contract_test.foo(0, 0, \'so\') == \'sothing\'
    assert contract_test.foo(0, 0, \'\') == 0

In order to fine tune test inputs generation, Klara integrates well with icontract. It will statically read the icontract decorator

import icontract

@icontract.require(lambda x: x > 100)
@icontract.ensure(lambda result: result > 200)
def foo(x: int, y: int, z: str):
    if x + y > 2:
        return x + y + 12
    elif x < y:
        return x + y
    elif (z + "me") == "some":
        return z + "thing"
    else:
        return x - y

Which will require that x argument is more than 100, and that the returned result is more than 200. Note that return z + “thing” at line 11 is returning a string, thus the constraint result > 200 is invalid. Klara is fault tolerant by design, thus any constraint that is invalid will be skipped with warnings. This will result in the following test case:

import foo


def test_foo_0():
    assert foo.foo(101, 88, '') == 201
    assert foo.foo(101, -99, 'so') == 'sothing'
    assert foo.foo(101, -100, '') == 201