[DOC][RFC] property-based testing #5
Description
Property-Based Testing in jserv/rbtree
The jserv/rbtree test suite leverages property-based testing (PBT) to verify the correctness, consistency, and robustness of its red-black tree implementation. PBT is achieved by encoding data structure invariants as executable specifications and systematically generating diverse test cases to check those invariants across a wide range of scenarios.
This document explains:
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How properties are specified and checked
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How test cases are generated
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How the framework validates correctness and detects subtle bugs
1. Specification Definition
jserv/rbtree defines four property types, each with a dedicated mechanism to check correctness:
| Property Type | Goal | rbtree Example |
|---|---|---|
| Classical | Maintain internal invariants | 5 red-black properties always hold |
| Round-trip | Operations cancel out or restore state | insert+delete = no-op |
| Catastrophic | No crash under bad input | Delete non-existent keys won't segfault |
| Differential | Cross-check correctness | Cached tree vs. Standard tree |
1.1 Classical Properties
The 5 classical red-black tree invariants are explicitly tested in multiple locations:
- Root is black
- Red nodes have black children
- Every path to a leaf has the same number of black nodes
- Nodes are in in-order traversal order
- If a node N has exactly one child, the child must be red
The Classical Properties for binary search tree
- For every node, all values in its left subtree are less than the node's value, and all values in its right subtree are greater than the node's value