Testing python code

Question

I want to test a python code that gets inputs from a different function (eg MeasureRadius). MeasureRadius is not ready because it relies on an instrument that I haven't receive yet. What's the best way to test CalculateArea with different values on iRadius, and iErrorCode outputted from MeasureRadius? An automated way will be nice. I was going to use unittest, but I don't know how I would change iRadius and iErrorCode returned from MeasureRadius.

class Instrument():
 def MeasureRadius(self):
 iErrorCode = 0
 sErrorMsg = ""
 iRadius = 0
 try:
 #tell the instrument to measure param A, the measurement goes into iRadius param
 #iRadius = Measure() 
 except:
 sErrorMsg = "MeasureRadius caught an exception."
 iErrorCode = 1
 return iRadius, iErrorCode, sErrorMsg
def CalculateArea():
 """calculate area from the measured radius. Returns area, error code, error message"""
 iRadius, iErrorCode, sErrorMsg = Instrument.MeasureRadius()
 if iErrorCode != 0:
 return 0.0,iErrorCode, sErrorMsg
 if iRadius <1 :
 return 0.0,1, "Radius too small."
 fArea = 3.14*iRadius*iRadius
 return fArea,0,""

• S.Lott: Your indentation is very hard to read. At least 3 spaces. Ideally 4. You have a method function def MeasureRadius with an Upper Case name, which is also a bad idea.

Answer 1

You need a "Mock fixture" that replaces the Instrument class.

You also need to redesign CalculateArea so it's testable.

def CalculateArea( someInstrument ):
 iRadius, iErrorCode, sErrorMsg = someInstrument.measureRadius()
 # rest of this is the same.
class MockInstrument( object ):
 def __init__( self, iRadius, iErrorCode, sErrorMsg ):
 self.iRadius= iRadius
 self.iErrorCode= iErrorCode
 self.sErrorMsg= sErrorMsg
 def measureRadius( self ):
 return self.iRadius, self.iErrorCode, self.sErrorMsg
class TestThisCondition( unittest.TestCase ):
 def setUp( self ):
 x = MockInstrument( some set of values )
 def test_should_do_something( self ):
 area, a, b = CalculateArea( x )
 assert equality for the various values.