The purpose of this workshop is to introduce Property Based Testing with Fast-Check. The workshop is based off of the Kata on Chapter 6 of Property-Based Testing with PropEr, Erlang, and Elixir by Fred Hebert. I highly recommend this book.
Given the following table:
| Item | Unit Price | Special Price |
|---|---|---|
| A | 50 | 3 for 130 |
| B | 30 | 2 for 45 |
| C | 20 | |
| D | 15 |
Given a item price catalog, when given a list of items to purchase, then calculate the total. This project provides a sample skeleton, but feel free to adjust the code as needed.
- Item names are unique
- List of items have no set length
- List of items are unordered
- Unit prices are whole numbers
- All items have a unit price
- Special prices can be applied multiple times
- Special prices are optional
Property based testing frameworks check the truthfulness of properties. A property is a statement like: for all (x, y, ...) such as precondition(x, y, ...) holds property(x, y, ...) is true. -
fast-checkdocs
As a group, let's identify the properties of this function:
Here are some patterns from the Quick Theories documentation.
- Invariant Pattern "Some things never change"
- The inverse function pattern "There and back again"
- Idempotence "The more things change, the more they stay the same"
- Analogous function pattern "Different paths same destination"
Working with the fast-check basic arbitraries, create a generator to generate a random item.
Using the total.spec.ts, test a property that you defined in Step 1. If you finish early, test more properties.
- Try configuring
fast-checkto run through more or fewer examples.
- Identify very, very broad properties
- Apply very, very broad inputs to verify that the system doesn't crash