Unit testing failing due to 0.000000001f inaccuarcy

Question

A vector is out by 0.000000001f so the test is failing.

Doing the logic in my head yeilds -1.0f, -1.0f but when I wrote the code to pass the test (Using the built in Vector methods) the answer comes back as -0.999999999f, -0.999999999f which is still 'right'.

This is C# (Vector2 class provided by the XNA framework) by the way, so I tried adding an epsilon value to each the x and y parameter of the Vector but this didn't work.

The way I see it is that by coding the answer, I'm writing the production code. E.g. it would be the same. Surely this is not the right.

Any advice?

Answer 1

Unit testing frameworks usually provide asserts for floats that take a precision. For example in Visual Studio Test you can write:

Assert.AreEqual(1.0f, 0.9999999999f, 1e-3); // passes
Assert.AreEqual(1.0f, 0.9f, 1e-3); // fails

Answer 2

Please see my answer here.

It is not about C#, but the same logic applies.