Part 11 – Property Tests
This is a series of posts I’m writing about using types as another tool in software development, Continuous Delivery, & keeping LLM’s honest. They’re also a design & refactoring tool, a communication tool, and reduce how many tests you have to write.
Parts
- Part 1 – Branded Types
- Part 2 – Product Types
- Part 3 – Union & Discriminated Unions
- Part 4 – Non-Empty Collections
- Part 5 – Indexed Types
- Part 6 – unknown vs any
- Part 7 – Result
- Part 8 – Schema
- Part 9 – Total Function
- Part 10 – Errors as Values
- Part 11 – Property Tests
- Part 12 – Type Proofs
- Part 13 – Exhaustiveness Checking
- Part 14 – Parse, Don’t Validate
- Part 15 – Anti-Corruption Layer
- Part 16 – Opaque Types
- Part 17 – Maybe
- Part 18 – Smart Constructors
- Part 19 – Pipeline
- Part 20 – Railway Oriented Programming
- Part 21 – Typestate
- Part 22 – Capabilities
- Part 23 – Immutability
- Part 24 – Making Impossible States Impossible
- Part 25 – Type Driven Development: How to do it
- Part 26 – Final Thoughts
We’ve got more than enough type knowledge to build total functions. Type safety is a spectrum; is there a way to determine how total our functions are? A few. One particular way is to utilize Property Tests. You write a single unit test, it generates 100 random inputs. If one of those inputs fails, it’ll give you the random seed so you can test the exact sequence of inputs yourself (e.g. fast-check, jsverify):
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