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Property-Based Testing with Hypothesis

使用Hypothesis进行基于属性的测试

Discover edge cases automatically by testing properties instead of examples.
通过测试属性而非具体示例，自动发现边界情况。

Overview

概述

  • Testing functions with many possible inputs
  • Validating invariants that must hold for all inputs
  • Finding boundary conditions and edge cases
  • Testing serialization/deserialization roundtrips
  • Stateful testing of APIs and state machines
  • 测试存在大量可能输入的函数
  • 验证对所有输入都成立的不变量
  • 寻找边界条件和极端场景
  • 测试序列化/反序列化往返流程
  • 对API和状态机进行有状态测试

Quick Reference

快速参考

Example-Based vs Property-Based

基于示例的测试 vs 基于属性的测试

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Example-based: Test specific inputs

基于示例：测试特定输入

def test_sort_examples(): assert sort([3, 1, 2]) == [1, 2, 3] # But what about [-1], [1.5, 2.5], ...?
def test_sort_examples(): assert sort([3, 1, 2]) == [1, 2, 3] # 但像[-1]、[1.5,2.5]这些情况呢？

Property-based: Test properties for ALL inputs

基于属性：测试适用于所有输入的属性

from hypothesis import given from hypothesis import strategies as st
@given(st.lists(st.integers())) def test_sort_properties(lst): result = sort(lst) assert len(result) == len(lst) # Same length assert all(result[i] <= result[i+1] for i in range(len(result)-1)) # Ordered

See [strategies-guide.md](references/strategies-guide.md) for complete strategy reference.
from hypothesis import given from hypothesis import strategies as st
@given(st.lists(st.integers())) def test_sort_properties(lst): result = sort(lst) assert len(result) == len(lst) # 长度一致 assert all(result[i] <= result[i+1] for i in range(len(result)-1)) # 结果有序

完整的策略参考请查看[strategies-guide.md](references/strategies-guide.md)。

Common Strategies

常用策略

python
from hypothesis import strategies as st

st.integers(min_value=0, max_value=100)  # Bounded integers
st.text(min_size=1, max_size=50)         # Bounded text
st.lists(st.integers(), max_size=10)     # Bounded lists
st.from_regex(r"[a-z]+@[a-z]+\.[a-z]+")  # Pattern-based
python
from hypothesis import strategies as st

st.integers(min_value=0, max_value=100)  # 有界整数
st.text(min_size=1, max_size=50)         # 有界文本
st.lists(st.integers(), max_size=10)     # 有界列表
st.from_regex(r"[a-z]+@[a-z]+\.[a-z]+")  # 基于正则模式

Composite for domain objects

用于领域对象的复合策略

@st.composite def user_strategy(draw): return User( name=draw(st.text(min_size=1, max_size=50)), age=draw(st.integers(min_value=0, max_value=150)), )
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@st.composite def user_strategy(draw): return User( name=draw(st.text(min_size=1, max_size=50)), age=draw(st.integers(min_value=0, max_value=150)), )
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Common Properties

常用属性

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Roundtrip (encode/decode)

往返测试（编码/解码）

@given(st.dictionaries(st.text(), st.integers())) def test_json_roundtrip(data): assert json.loads(json.dumps(data)) == data
@given(st.dictionaries(st.text(), st.integers())) def test_json_roundtrip(data): assert json.loads(json.dumps(data)) == data

Idempotence

幂等性

@given(st.text()) def test_normalize_idempotent(text): assert normalize(normalize(text)) == normalize(text)
@given(st.text()) def test_normalize_idempotent(text): assert normalize(normalize(text)) == normalize(text)

Oracle (compare to known implementation)

参照测试（与已知实现对比）

@given(st.lists(st.integers())) def test_sort_matches_builtin(lst): assert our_sort(lst) == sorted(lst)

See [stateful-testing.md](references/stateful-testing.md) for state machine testing.
@given(st.lists(st.integers())) def test_sort_matches_builtin(lst): assert our_sort(lst) == sorted(lst)

状态机测试相关内容请查看[stateful-testing.md](references/stateful-testing.md)。

Key Decisions

关键决策

DecisionRecommendation
Strategy designComposite strategies for domain objects
Example count100 for CI, 10 for dev, 1000 for release
Database testsUse explicit mode, limit examples
DeadlineDisable for slow tests, 200ms default
Stateful testsRuleBasedStateMachine for state machines
决策项推荐方案
策略设计为领域对象使用复合策略
示例数量CI环境用100个，开发环境用10个，发布环境用1000个
数据库测试使用显式模式，限制示例数量
超时时间慢测试禁用，默认200毫秒
有状态测试为状态机使用RuleBasedStateMachine

Anti-Patterns (FORBIDDEN)

反模式（禁止使用）

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NEVER ignore failing examples

绝对不要忽略失败的示例

@given(st.integers()) def test_bad(x): if x == 42: return # WRONG - hiding failure!
@given(st.integers()) def test_bad(x): if x == 42: return # 错误 - 隐藏了失败情况！

NEVER use filter with low hit rate

绝对不要使用命中率极低的filter

st.integers().filter(lambda x: x % 1000 == 0) # WRONG - very slow
st.integers().filter(lambda x: x % 1000 == 0) # 错误 - 速度极慢

NEVER test with unbounded inputs

绝对不要使用无界输入进行测试

@given(st.text()) # WRONG - includes 10MB strings def test_username(name): User(name=name)
@given(st.text()) # 错误 - 会生成10MB大小的字符串 def test_username(name): User(name=name)

NEVER mutate strategy results

绝对不要修改策略生成的结果

@given(st.lists(st.integers())) def test_mutating(lst): lst.append(42) # WRONG - mutates generated data
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@given(st.lists(st.integers())) def test_mutating(lst): lst.append(42) # 错误 - 修改了生成的数据
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Related Skills

相关技能

  • pytest-advanced
    - Custom markers and parallel execution
  • unit-testing
    - Basic testing patterns
  • contract-testing
    - API contract testing with Pact
  • pytest-advanced
    - 自定义标记与并行执行
  • unit-testing
    - 基础测试模式
  • contract-testing
    - 使用Pact进行API契约测试

References

参考资料

  • Strategies Guide - Complete strategy reference
  • Stateful Testing - State machine patterns
  • Hypothesis Conftest - Production setup
  • 策略指南 - 完整的策略参考
  • 有状态测试 - 状态机模式
  • Hypothesis Conftest - 生产环境配置

Capability Details

能力详情

strategies

strategies

Keywords: strategy, hypothesis, generator, from_type, composite Solves: Generate test data, create strategies for custom types
关键词: strategy, hypothesis, generator, from_type, composite 解决问题: 生成测试数据，为自定义类型创建策略

properties

properties

Keywords: property, invariant, roundtrip, idempotent, oracle Solves: What properties to test, roundtrips, invariants
关键词: property, invariant, roundtrip, idempotent, oracle 解决问题: 确定测试属性、往返测试、不变量验证

stateful

stateful

Keywords: stateful, state machine, RuleBasedStateMachine, rule Solves: Test stateful systems, model state transitions
关键词: stateful, state machine, RuleBasedStateMachine, rule 解决问题: 测试有状态系统，建模状态转换

schemathesis

schemathesis

Keywords: schemathesis, openapi, api testing, fuzzing Solves: Fuzz test API endpoints, generate from OpenAPI spec
关键词: schemathesis, openapi, api testing, fuzzing 解决问题: 模糊测试API端点，根据OpenAPI规范生成测试用例

hypothesis-settings

hypothesis-settings

Keywords: max_examples, deadline, profile, suppress_health_check Solves: Configure for CI vs dev, speed up slow tests
关键词: max_examples, deadline, profile, suppress_health_check 解决问题: 为CI与开发环境配置参数，加速慢测试