Setup & First Tests — Pytest for Python Testing | Sabaoon Academy

pytest is the most widely used Python testing framework. It requires no boilerplate classes — just write functions starting with test_ and run pytest.

Installation

pip install pytest

Verify:

pytest --version

Your First Tests

# test_math.py

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

def test_add_positive():
    assert add(2, 3) == 5

def test_add_negative():
    assert add(-1, -1) == -2

def test_add_zero():
    assert add(0, 10) == 10

Run:

pytest test_math.py -v

Output:

test_math.py::test_add_positive PASSED
test_math.py::test_add_negative PASSED
test_math.py::test_add_zero     PASSED

Test Discovery Rules

pytest automatically finds tests that match:

Rule	Example
Files named `test_.py` or `_test.py`	`test_auth.py`, `auth_test.py`
Functions starting with `test_`	`def test_login():`
Methods starting with `test_` in `Test*` classes	`class TestAuth: def test_login(self):`

Run pytest in a directory to discover all matching tests recursively.

Assertion Introspection

pytest rewrites assert statements to show detailed failure messages:

def test_greeting():
    result = "Hello, World"
    assert result == "Hello, World!"

AssertionError: assert 'Hello, World' == 'Hello, World!'
  - Hello, World!
  ? ^
  + Hello, World

No assertEqual, assertTrue, or custom matchers needed — plain assert is enough.

Test Lifecycle Visualiser

pytest discovery and execution

Ctrl+Enter

HTML

CSS

var files = [
{ name: 'helpers.py',       match: false },
{ name: 'test_math.py',     match: true  },
{ name: 'config.py',        match: false },
{ name: 'test_string.py',   match: true  },
{ name: 'auth_test.py',     match: true  },
];

var tests = [
{ file: 'test_math.py',   name: 'test_add_positive',  pass: true  },
{ file: 'test_math.py',   name: 'test_add_negative',  pass: true  },
{ file: 'test_string.py', name: 'test_upper',          pass: true  },
{ file: 'test_string.py', name: 'test_strip',          pass: false },
{ file: 'auth_test.py',   name: 'test_login',          pass: true  },
];

var container = document.getElementById('files');
files.forEach(function(f) {
var div = document.createElement('div');
div.className = 'file';
div.id = 'f-' + f.name;
div.textContent = f.name;
container.appendChild(div);
});

document.getElementById('discoverBtn').onclick = function() {
var out = document.getElementById('output');
out.innerHTML = '';
this.disabled = true;

// Phase 1: discovery
var i = 0;
function discover() {
  if (i >= files.length) { setTimeout(runTests, 300); return; }
  var f = files[i];
  var el = document.getElementById('f-' + f.name);
  if (f.match) { el.classList.add('found'); }
  i++;
  setTimeout(discover, 180);
}

function append(cls, text) {
  var span = document.createElement('span');
  span.className = cls;
  span.textContent = text + '\n';
  out.appendChild(span);
}

Preview

Organising Tests in Classes

class TestStringMethods:
    def test_upper(self):
        assert "hello".upper() == "HELLO"

    def test_strip(self):
        assert "  hello  ".strip() == "hello"

    def test_split(self):
        s = "hello world"
        assert s.split() == ["hello", "world"]

Classes don't need to inherit from anything — just prefix them with Test.

Running Specific Tests

pytest test_math.py::test_add_positive   # single test
pytest -k "add"                          # tests matching "add" in name
pytest -k "not slow"                     # exclude by name
pytest -x                                # stop on first failure
pytest -v                                # verbose output