Biocomputing II
Unit Testing
Prof. Andrew C.R. Martin, UCL
- View the lecture on YouTube
- Download as an MP4 video file
Introduction
Unit testing:
- A very important concept in all languages
- Like version control, it is often missing from introductory programming courses
- Here we focus on Python, but the concepts are general
- Testing and test-driven design
What is Unit Testing?
"A method of testing individual 'units' of source code to determine whether they are fit for use"
- Unit testing requires modular design of your code
- Smaller subroutines/methods are easier to test
- More testing = fewer bugs!
Why do it?
- Individual subroutines are easier to test than whole programs
- Unit tests can be standardized and automated
- Automated testing allows extensive testing after changes are made to code
- Tests also act as documentation for your code
Anatomy of a test
A simple example
#!/usr/bin/env python3
# --------------------------------------------------------------------------
def signedSquare(val):
"""Returns the square of a number, but if the number was negative
the returned value is also negative
Input: val A number to be squared
Return: the signed square of the number
"""
# Simple way of doing it - not very neat
if(val < 0):
sign = -1
else:
sign = 1
# Let's try the 'Conditional expressions' approach instead
# sign = -1 if val < 0 else 1
square = val * val
return(sign * square)
# --------------------------------------------------------------------------
# Test code
if __name__ == "__main__":
val = signedSquare(2)
if(val != 4):
print("signedSquare(2) failed")
else:
print("signedSquare(2) success")
val = signedSquare(0)
if(val != 0):
print("signedSquare(0) failed")
else:
print("signedSquare(0) success")
val = signedSquare(-2)
if(val != -4):
print("signedSquare(-2) failed")
else:
print("signedSquare(-2) success")
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Doing it better
#!/usr/bin/env python3
# --------------------------------------------------------------------------
def signedSquare(val):
"""Returns the square of a number, but if the number was negative
the returned value is also negative
Input: val A number to be squared
Return: the signed square of the number
"""
sign = -1 if val < 0 else 1
square = val * val
return(sign * square)
# --------------------------------------------------------------------------
def runTestOneReturn(name, input, expected, actual):
"""Run a test on a subroutine that returns a single value.
Input is:
name - the name of the subroutine being tested
input - the input to that subroutine (in quotes if more than one item)
expected - the expected output from the subroutine
actual - the actual output from the subroutine
"""
if(expected == actual):
print("Success: %s(%s)" % (name, input))
else:
print("Fail: %s(%s) - expected %s, obtained %s" %
(name, input, expected, actual))
# --------------------------------------------------------------------------
def test_signedSquare():
"""Run tests on the signedSquare() routine"""
runTestOneReturn("signedSquare", 2, 4, signedSquare(2))
runTestOneReturn("signedSquare", 0, 0, signedSquare(0))
runTestOneReturn("signedSquare", -2, -4, signedSquare(-2))
# --------------------------------------------------------------------------
# MAIN PROGRAM: Run a set of tests
if __name__ == "__main__":
test_signedSquare()
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