A good way to write unit tests
- by bobobobo
So, I previously wasn't really in the practice of writing unit tests - now I kind of am and I need to check if I'm on the right track.
Say you have a class that deals with math computations.
class Vector3
{
public: // Yes, public.
float x,y,z ;
// ... ctors ...
} ;
Vector3 operator+( const Vector3& a, const Vector3 &b )
{
return Vector3( a.x + b.y /* oops!! hence the need for unit testing.. */,
a.y + b.y,
a.z + b.z ) ;
}
There are 2 ways I can really think of to do a unit test on a Vector class:
1) Hand-solve some problems, then hard code the numbers into the unit test and pass only if equal to your hand and hard-coded result
bool UnitTest_ClassVector3_operatorPlus()
{
Vector3 a( 2, 3, 4 ) ;
Vector3 b( 5, 6, 7 ) ;
Vector3 result = a + b ;
// "expected" is computed outside of computer, and
// hard coded here. For more complicated operations like
// arbitrary axis rotation this takes a bit of paperwork,
// but only the final result will ever be entered here.
Vector3 expected( 7, 9, 11 ) ;
if( result.isNear( expected ) )
return PASS ;
else
return FAIL ;
}
2) Rewrite the computation code very carefully inside the unit test.
bool UnitTest_ClassVector3_operatorPlus()
{
Vector3 a( 2, 3, 4 ) ;
Vector3 b( 5, 6, 7 ) ;
Vector3 result = a + b ;
// "expected" is computed HERE. This
// means all you've done is coded the
// same thing twice, hopefully not having
// repeated the same mistake again
Vector3 expected( 2 + 5, 6 + 3, 4 + 7 ) ;
if( result.isNear( expected ) )
return PASS ;
else
return FAIL ;
}
Or is there another way to do something like this?
