COMP1531

1.5 - SDLC Testing - Intro

In this lecture

Basics of pytest (to test code)
Understanding importing and paths

C-Style Testing

How did you test in COMP1511?

#include <stdio.h>
#include <assert.h>

double sum(double a, double b) {
    return a + b;
}

int main() {
    assert(sum(1, 2) == 3);
    assert(sum(2, 2) == 4);
    assert(sum(3, 2) == 5);
    printf("All tests passed\n");
}

ctest.c

Let's first look at python functions

double sum(double a, double b) {
    return a + b;
}

def sum(a, b):
    return a + b

Q. What are the key differences?

C-Style Testing

Let's first look at python functions

double sum(double a, double b) {
    return a + b;
}

def sum(a, b):
    return a + b

Q. What are the key differences?

No semi-colons
No braces
No typing
"def" to say define function

C-Style Testing

Q. How would we test this python function?

def sum(a, b):
    return a + b

C-Style Testing

Q. How would we test this python function?

def sum(a, b):
    return a + b

assert sum(1, 4) == 3

cstyletest.c

C-Style Testing

Let's clean this up and wrap it in a function, though!

def sum(a, b):
    return a + b

def testSmallNumbers():
    assert sum(1, 4) == 3
    
testSmallNumbers()

C-Style Testing

Basic Python testing

Let's take a look at pytest

What is pytest?

pytest is a library that helps us write small tests, but can also be used to write larger and more complex tests
pytest comes with a binary that we run on command line
pytest detects any function prefixed with test and runs that function, processing the assertions inside

pytest - basic

def sum(x, y):
    return x * y

def test_sum1():
    assert sum(1, 2) == 3

test_sum1()

$ python3 test1_nopytest.py

test1_nopytest.py

import pytest

def sum(x, y):
    return x * y

def test_sum1():
    assert sum(1, 2) == 3, "1 + 2 == 3"

$ pytest test1_pytest.py

test1_pytest.py

pytest - more complicated

import pytest

def sum(x, y):
    return x + y

def test_small():
    assert sum(1, 2) == 3, "1, 2 == "
    assert sum(3, 5) == 8, "3, 5 == "
    assert sum(4, 9) == 13, "4, 9 == "

def test_small_negative():
    assert sum(-1, -2) == -3, "-1, -2 == "
    assert sum(-3, -5) == -8, "-3, -5 == "
    assert sum(-4, -9) == -13, "-4, -9 == "

def test_large():
    assert sum(84*52, 99*76) == 84*52 + 99*76, "84*52, 99*76 == "
    assert sum(23*98, 68*63) == 23*98 + 68*63, "23*98, 68*63 == "

A more complicated test

test_multiple.py

pytest - prefixes

If you just run

$ pytest

Without any files, it will automatically look for any files in that directory in shape:

test_*.py
*_test.py

pytest - particular files

You can run specific functions without your test files with the -k command. For example, we if want to run the following:

test_small
test_small_negative
~~test_large~~

We could run

$ pytest -k small

or try

$ pytest -k small -v

pytest - markers

We can also use a range of decorators to specify tests in python:

import pytest

def pointchange(point, change):
	x, y = point
	x += change	
	y += change	
	return (x, y)

@pytest.fixture
def supply_point():
	return (1, 2)

@pytest.mark.up
def test_1(supply_point):
	assert pointchange(supply_point, 1) == (2, 3)

@pytest.mark.up
def test_2(supply_point):
	assert pointchange(supply_point, 5) == (6, 7)

@pytest.mark.up
def test_3(supply_point):
	assert pointchange(supply_point, 100) == (101, 102)

@pytest.mark.down
def test_4(supply_point):
	assert pointchange(supply_point, -5) == (-4, -3)

@pytest.mark.skip
def test_5(supply_point):
	assert False == True, "This test is skipped"

@pytest.mark.xfail
def test_6(supply_point):
	assert False == True, "This test's output is muted"

pytest - more

There are a number of tutorials online for pytest. This is a very straightforward one.