ordeal 0.1.3

Automated chaos testing for Python — fault injection, property assertions, and stateful exploration.

ordeal

Automated chaos testing for Python. Fault injection, property assertions, coverage-guided exploration, and stateful testing — in one library.

ordeal snaps together ideas from Antithesis (deterministic exploration + checkpointing), FoundationDB (BUGGIFY inline faults), Jepsen (nemesis interleaving), Hypothesis (stateful property testing), Jane Street's QuickCheck (boundary-biased generation), and Meta's ACH (mutation validation) into a single Python toolkit.

pip install ordeal

Quick start

1. Write a chaos test

from ordeal import ChaosTest, rule, invariant, always
from ordeal.faults import timing, numerical

class MyServiceChaos(ChaosTest):
    faults = [
        timing.timeout("myapp.api.call"),
        numerical.nan_injection("myapp.model.predict"),
    ]

    def __init__(self):
        super().__init__()
        self.service = MyService()

    @rule()
    def call_service(self):
        result = self.service.process("input")
        always(result is not None, "process never returns None")

    @invariant()
    def no_corruption(self):
        for item in self.service.results:
            always(not math.isnan(item), "no NaN in output")

# Hypothesis explores rule sequences + fault schedules
TestMyServiceChaos = MyServiceChaos.TestCase

2. Run with pytest

pytest --chaos                    # enable chaos mode
pytest --chaos --chaos-seed 42    # reproducible

3. Or explore with coverage guidance

ordeal explore                    # reads ordeal.toml
ordeal explore -v --max-time 300  # live progress, 5 minutes
ordeal replay .ordeal/traces/fail-run-42.json  # reproduce a failure

Install

# From PyPI
pip install ordeal

# With extras
pip install ordeal[atheris]    # coverage-guided fuzzing
pip install ordeal[api]        # API chaos testing via Schemathesis
pip install ordeal[all]        # everything

# As a CLI tool (no venv needed)
uv tool install ordeal         # global install, `ordeal` on PATH
uvx ordeal explore             # ephemeral, no install

# Development
git clone https://github.com/teilomillet/ordeal
cd ordeal
uv sync
uv run pytest                  # 205 tests
uv run ordeal explore          # run the explorer

What's in the box

Stateful chaos testing

ChaosTest extends Hypothesis's RuleBasedStateMachine. You declare faults and rules — ordeal auto-injects a nemesis rule that toggles faults during exploration. Hypothesis explores which faults fire, when, in what order, interleaved with your application rules.

from ordeal import ChaosTest, rule, invariant
from ordeal.faults import io, numerical, timing

class StorageChaos(ChaosTest):
    faults = [
        io.error_on_call("myapp.storage.save", IOError),
        timing.intermittent_crash("myapp.worker.process", every_n=3),
        numerical.nan_injection("myapp.scoring.predict"),
    ]
    swarm = True  # random fault subsets per run — better coverage

    @rule()
    def write_data(self):
        self.service.save({"key": "value"})

    @rule()
    def read_data(self):
        result = self.service.load("key")
        always(result is not None, "reads never return None after write")

Property assertions (Antithesis model)

Four assertion types, inspired by Antithesis:

from ordeal import always, sometimes, reachable, unreachable

always(len(results) > 0, "never empty")        # must hold every time
sometimes(cache_hit, "cache is exercised")      # must hold at least once
reachable("error-recovery-path")                # code path must execute
unreachable("silent-data-corruption")           # code path must never execute

always and unreachable raise immediately (triggering Hypothesis shrinking). sometimes and reachable are checked at the end of the session via the property report.

Inline fault injection (FoundationDB BUGGIFY)

Place buggify() calls in your production code. They're no-ops normally, and probabilistically return True during chaos testing:

from ordeal.buggify import buggify, buggify_value

def process(data):
    if buggify():
        time.sleep(random.random() * 5)       # sometimes slow
    result = compute(data)
    return buggify_value(result, float('nan')) # sometimes corrupt

Seed-controlled, thread-local, zero-cost in production.

Coverage-guided exploration

The Explorer is ordeal's answer to Antithesis's exploration engine. It uses AFL-style edge coverage to checkpoint interesting states, then branches from them:

from ordeal.explore import Explorer

explorer = Explorer(
    MyServiceChaos,
    target_modules=["myapp"],
    checkpoint_strategy="energy",  # favor productive checkpoints
)
result = explorer.run(max_time=60)
print(result.summary())
# Exploration: 5000 runs, 52000 steps, 60.0s
# Coverage: 287 edges, 43 checkpoints
# Failures found: 2
#   Run 342, step 15: ValueError: NaN in output (3 steps)

When a failure is found, the explorer shrinks it to the minimal reproducing sequence — delta debugging + single-step elimination + fault simplification.

TOML configuration

# ordeal.toml
[explorer]
target_modules = ["myapp"]
max_time = 60
seed = 42
checkpoint_strategy = "energy"

[[tests]]
class = "tests.test_chaos:MyServiceChaos"

[report]
format = "both"
traces = true
verbose = true

One file, versionable, shareable between humans and AI agents. See ordeal.toml.example for the full schema.

QuickCheck with boundary bias

@quickcheck infers strategies from type hints and biases toward boundary values (0, -1, empty list, max length) where bugs cluster:

from ordeal.quickcheck import quickcheck

@quickcheck
def test_sort_idempotent(xs: list[int]):
    assert sorted(sorted(xs)) == sorted(xs)

@quickcheck
def test_score_bounded(x: float, y: float):
    result = score(x, y)
    assert 0 <= result <= 1

Works with dataclasses, Optional, Union, nested types.

Composable invariants

from ordeal.invariants import no_nan, no_inf, bounded, finite

valid_score = finite & bounded(0, 1)
valid_score(model_output)  # raises AssertionError with clear message

Simulation primitives (no-mock testing)

from ordeal.simulate import Clock, FileSystem

clock = Clock()
fs = FileSystem()
service = MyService(clock=clock, fs=fs)

clock.advance(3600)                      # instant — no real waiting
fs.inject_fault("/data.json", "corrupt") # reads return random bytes

Mutation testing

Validates that your chaos tests actually catch bugs. AST-based operators (arithmetic, comparison, negate, return_none):

from ordeal.mutations import mutate_function_and_test

result = mutate_function_and_test("myapp.scoring.compute", my_tests)
print(result.summary())
# Mutation score: 15/18 (83%)
#   SURVIVED  L42:8 + -> -
#   SURVIVED  L67:4 negate if-condition

Fault primitives

from ordeal.faults import io, numerical, timing

io.error_on_call("mod.func")           # raise IOError
io.return_empty("mod.func")            # return None
io.truncate_output("mod.func", 0.5)    # truncate to half length
io.disk_full()                          # writes fail with ENOSPC
numerical.nan_injection("mod.func")     # output becomes NaN
numerical.inf_injection("mod.func")     # output becomes Inf
numerical.wrong_shape("mod.func", (1,512), (1,256))
timing.timeout("mod.func", delay=30)    # raise TimeoutError
timing.slow("mod.func", delay=2.0)      # add real delay
timing.intermittent_crash("mod.func", every_n=3)
timing.jitter("mod.func", magnitude=0.01)

Integrations

Atheris (coverage-guided fuzzing):

from ordeal.integrations.atheris_engine import fuzz
fuzz(my_function, max_time=60)  # coverage guides buggify decisions

Schemathesis (API chaos testing):

from ordeal.integrations.schemathesis_ext import chaos_api_test
chaos_api_test("http://localhost:8080/openapi.json", faults=[...])

CLI

ordeal explore                          # run from ordeal.toml
ordeal explore -c ci.toml -v            # custom config, verbose
ordeal explore --max-time 300 --seed 99 # override settings
ordeal replay trace.json                # reproduce a failure
ordeal replay --shrink trace.json       # minimize a failure trace

Install the CLI globally with uv tool install ordeal or run ephemerally with uvx ordeal explore.

Architecture

ordeal/
├── chaos.py           ChaosTest + nemesis + swarm            Hypothesis + Jepsen
├── explore.py         Coverage-guided explorer               Antithesis
├── assertions.py      always/sometimes/reachable             Antithesis
├── buggify.py         Inline fault injection                 FoundationDB
├── quickcheck.py      @quickcheck + boundary bias            Jane Street
├── simulate.py        Clock, FileSystem                      Jane Street
├── invariants.py      Composable: no_nan & bounded(0,1)
├── mutations.py       AST mutation testing                   Meta ACH
├── trace.py           Trace recording + shrinking
├── config.py          TOML configuration
├── cli.py             ordeal explore / replay
├── plugin.py          pytest --chaos
├── strategies.py      Adversarial data generation
├── faults/            io, numerical, timing
└── integrations/      atheris, schemathesis

Design constraint

If an LLM can generate a working chaos test from reading source code alone — no implicit knowledge, no undocumented conventions — then it's automatically easy for humans too. The LLM constraint forces clarity: explicit fault registration, declarative rules, zero hidden setup.

License

Apache 2.0