Question

I am new to unit testing/TDD and having problem getting my head certain aspects of it. For example I am not sure how complete the tests should be imagine the following scenario.

I am writing a test to ensure I get the correct prices for a product. A product can come in different sizes and bought in a number of defined quantities. The price of the product will reflect the size and quantity.

For example:

Product A has the pricing matrix below (quantity down the side and size along the top)

----------------------------
|     | xs |  s |  m |  l  | 
----------------------------
|  250| 10 | 20 | 50 | 100 | 
----------------------------
|  500| 20 | 40 | 60 | 110 | 
----------------------------
| 1000| 15 | 25 | 55 | 105 | 
----------------------------
| 1500| 12 | 22 | 52 | 102 | 
----------------------------

Now say I was writing tests for a class method

Pricer.GetPrice(Product p, string size, int quantity)

Should I test for every product/size/quantity combo? as you can imagine this could mean a large number of tests.

If the prices are sourced from a data store and thus liable to change how do you keep your tests correct or is that just a annoying by product?

Also does anyone have any good links to read regarding writing tests/TDD. Maybe going through CRUD/Repositories as this seems a bit of a chicken and egg type scenario.

Answer 1

It sounds like there are two elements to your pricing logic.

1. A price matrix data structure mapping (size, quantity cutoff) pairs to prices.

2. A function that takes a price matrix and a Product instance and returns a price.

Testing the price matrix is meaningless; the numbers are arbitrary. If you feel you need to test the function, I would pass it different fake, hard-coded test matrices with different mock products and test to verify that the right price comes out. The most relevant edge cases are probably when you ask for a price for a cutoff quantity exactly or off-by-one from one.