def main():
x = int(input("What's x? "))
print("x squared is", square(x))
def square(n):
return n * n
if __name__ == "__main__":
main()Note that the
if__name__ == "__main__":statement should be used to call main() in every program from now on.
from calculator import square
def main():
test_square()
def test_square():
if square(2) != 4:
print("2 squared was not 4")
if square(3) != 9:
print("3 squared was not 9")
if __name__ == "__main__":
main()Notice we are importing the square() function from calculator.py. The convention is to create a function called test_square(). Inside that function we define conditions to test.
This method can be limited by corner cases and is lengthy, we have written more code to test than to write the program.
Python's assert command allows us to tell the compiler that something, some assertion, is True.
from calculator import square
def main():
test_square()
def test_square():
assert square(2) == 4
assert square(3) == 9
if __name__ == "__main__":
main()Using the assert keyword will reduce code lines. If the assertion is True, nothing will happen. If the assertion is False, we will get an
AssertionError.
from calculator import square
def main():
test_square()
def test_square():
try:
assert square(2) == 4
except AssertionError:
print("2 squared was not 4")
try:
assert square(3) == 9
except AssertionError:
print("3 squared was not 9")
try:
assert square(-2) == 4
except AssertionError:
print("-2 squared was not 4")
try:
assert square(-3) == 9
except AssertionError:
print("-3 squared was not 9")
try:
assert square(0) == 0
except AssertionError:
print("0 squared was not 0")Adding
try-exceptblocks will give a more user friendly output but comes with a major challenge. If we want to test for all possible cases we will need to cover all corner cases and end up with *dozens of try-except blocks.
pytest is a third-party library that allows you to unit test your program (docs.pytest.org).
pip install pytest
from calculator import square
def test_square():
assert square(2) == 4
assert square(3) == 9
assert square(-2) == 4
assert square(-3) == 9
assert square(0) == 0pytest allows us to run our program directly through it from the terminal window
pytest test_calculator.py
Inconclusive:
$ pytest test_calculator.py
test_calculator.py F [100%]
========================== FAILURES =======================
_________________________ test_square _____________________
def test_square():
assert square(2) == 4
> assert square(3) == 9
E assert 6 == 9
E + where 6 = square(3)
test_calculator.py:5: AssertionError
================= short test summary info ==================
FAILED test_calculator.py::test_square - assert 6 == 9
================== 1 failed in 0.16s =======================
Conclusive:
test_calculator.py . [100%]
====================== 1 passed in 0.01s ===================
from calculator import square
def test_positive():
assert square(2) == 4
assert square(3) == 9
def test_negative():
assert square(-2) == 4
assert square(-3) == 9
def test_zero():
assert square(0) == 0It is a good idea to divide the tests into groups in different functions. pytest will run each function automatically. This will return a diagnostic of each function allowing us to have more detailed clues on the bugs.
test_calculator.py ... [100%]
====================== 3 passed in 0.01s ===================
import pytest
from calculator import square
def test_positive():
assert square(2) == 4
assert square(3) == 9
def test_negative():
assert square(-2) == 4
assert square(-3) == 9
def test_zero():
assert square(0) == 0
def test_str():
with pytest.raises(TypeError):
square("cat")We import the pytest library to use the
pytest.raises()function, which allows us to express that we are expecting an error to be raised.
def main():
name = input("What's your name? ")
hello(name)
def hello(to="world"):
print("hello,", to)
if __name__ == "__main__":
main()from hello import hello
def test_hello():
hello("Lazer") == "hello, Lazer"Attempting to use this approach to test the code might not work because the hello() function does not return a value, it simply prints something.
# hello.py Version 2
def main():
name = input("What's your name? ")
print(hello(name))
def hello(to="world"):
return f"hello, {to}"
if __name__ == "__main__":
main()Notice how we changed hello() to
returninstead of print. And changed the main() function to handle the printing This will allow us to use pytest. We also changed the main() function to print(hello(name)).
# test_hello.py Version 2
from hello import hello
def test_hello():
hello("Lazer") == "hello, Lazer"Now that hello() returns a value, running pytest test_hello.py will work as expected.
# test_hello.py Version 3
from hello import hello
def test_default():
assert hello() == "hello, world"
def test_argument():
assert hello("Lazer") == "hello, Lazer"Dividing the test into different functions will allow us to test more effectively for each use case.
# Suppose we have a list of names. We can test as follows:
for name in ["Abraham", "Yitshak", "Yaacov"]:
assert hello(name) == f"hello, {name}"Unit testing code using multiple tests is so common that you have the ability to run a whole folder of tests with a single command.
mkdir test
code test/test_hello.py
In test_hello.py write test code
code test/__init__.py
Used to indicate that a directory should be treated as a package, facilitating organization, importation and discovery of test modules. The file can be empty.
def main():
while True:
au = input("AU: ")
try:
au = float(au)
break
except ValueError:
continue
print(f"{au} AU is {convert(au)} m")
def convert(au):
if not isinstance(au, (int, float)):
raise TypeError("AU must be an int or float")
return au * 149597870700
if __name__ == "__main__":
main()isinstance(au, (int, float)) returns True if
auis an integer or a loathing-point number. If not, the function raises aTypeError.
import pytest
from convert import convert
def test_conversion():
assert convert(1) == 149597870700
assert convert(50) == 7479893535000
def test_error():
with pytest.raises(TypeError):
convert("1")pytest.raises() takes the type exception as an argument and asserts that it is raised within the with block. convert("1") is the statement within the
withblock and takes the string1as an argument.
Since the convert() function checks if input is int or float and raises a
TypeErrorif not, passing string1will raise the exception.
# test_convert.py Version 2
import pytest
from convert import convert
def test_int_conversion():
assert convert(1) == 149597870700
assert convert(50) == 7479893535000
def test_error():
with pytest.raises(TypeError):
convert("1")
def test_float_conversion():
assert convert(0.001) == pytest.approx(149597870.691)Floating-point arithmetic can sometimes lead to very small differences due to precision issues.
pytest.approx(149597870.691)is used to allow a small margin of error in the comparison.
# test_float_conversion() Version 2
def test_float_conversion():
assert convert(0.001) == pytest.approx(149597870.691, abs=0.1)
abs=0.1This sets the tolerance level for the comparison. It means that the result of convert(0.001) should be within +/-0.1units of the expected value.
# test_float_conversion() Version 3
def test_float_conversion():
assert convert(0.001) == pytest.approx(149597870.691, abs=1e-5)
abs=1e-5This specifies that the difference between the actual result and the expected value should not exceed 1 x 10^-5 (or 0.00001).