Understanding unit testing for dynamically changing condition

Question

I was trying to understand how to write unit tests for a few days now. I'm confused with following scenarios in the existing code.

In first function the max value changes depending on the object created at run time but in the second case it is a constant.

NOTE: The following functions are not related. These are two different scenarios.

SomeFunction1(arg1,....)
{
  if(arg1 > someObject.MaxAllowedValue)
  {
     throw exception;
  }
}

SomeFunction2(arg1,....)
{
  if(arg1 > maxAllowedValue)
  {
     throw exception;
  }
}

I am trying to test whether the function throws an exception when max value is exceeded.

Does the unit test remain the same in both the cases or is it different?

Answer 1

That would depend somewhat on where someObject came from and how its property value changes. But assuming that someObject.MaxAllowedValue and maxAllowedValue have the same value, the test will remain the same. Remember, you are testing the behaviour of SomeFunctionX, not the implementation details.

Answer 2

TL;DR: 1) refactor your code 2) mock someObject

Refactor your code

Congraz, you are just unit testing for a few days now and have learned one of the most important aspects of unit testing (especially when done early in the development process):

The act of writing a unit test is more an act of design 
than of verification.  

(Uncle Bob, Agile Software Development, Principles, Patterns, and Practices)

So if SomeFunction1 and SomeFunction2 have closely related functionality and concerns, refactor them into one method. If not, you also need to write different unit tests for them since they cover different functionality/concerns.

Mock

If your code still contains

if(arg1 > someObject.MaxAllowedValue)

think about whether your current unit test should also test someObjects (probably not). If not, you should mock it, e.g. with EasyMock (this cheat sheet is helpful for both junit and EasyMock).

Update: Since you are testing another class, not that of someObject, it does not matter that someObject changes at runtime. All you have to do is cover all possible behaviors of your implementation under test with your tests, e.g.

• arg1 == someObject.MaxAllowedValue
• arg1 == someObject.MaxAllowedValue+1