Lesson 48 of 55
10 mins readPython Property-Based Testing with QuickCheck
In Plain English
QuickCheck revolutionizes software testing: instead of testing manually chosen sample inputs, you write mathematical properties (invariants) and QuickCheck generates hundreds of random test cases to verify them.
Deep Dive: How It Works
Property-Based Testing: Test universal rules such as reverse (reverse xs) == xs for all lists.
Automatic Shrinking: When QuickCheck finds a failing test case, it automatically shrinks the input to the smallest possible counterexample.
Arbitrary Typeclass: Generates pseudorandom values for testing custom data types.
Core Rules to Remember
Universal Invariants: Test properties that must hold true for all possible inputs.
Automated Counterexample Shrinking: Pinpoint edge cases instantly (e.g. empty lists, negative numbers).
Live Interactive Example
Hit Run Code to see it liveTesting Invariants with Property Functions
Python 3.12
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Output Console
Click "Run Code" to view the rendered output.
How it works: Both property functions validated the invariant properties.
Your Turn: Micro Challenge
No pressure! Edit the starter code below and test your solution with instant feedback.
Micro Exercise
Verify Sort Length Invariant
- Check if `length [3, 1, 2] == length [1, 2, 3]`.
- Print `"Invariant holds: "` followed by its `show` string.
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Sandbox Output
Click "Run & Check" to test your solution.
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