How To Run A Single Test In Pytest (Using CLI And Markers)

You’ve written code and Unit tests, and want to make sure it works. You simply run the pytest command in your terminal to run them the tests. Boom! some tests fail.

How do you debug it?

To debug, it’s sometimes helpful to run one test, run tests in a specific module or class, or run tests based on a marker.

Tests

The tests are stored in a separate files, typically in a directory named tests. Pytest will automatically discover these tests due to the test_ prefix in the filename and function names.

  
from operations.core import add_numbers, multiply_numbers  
import pytest  
  
def test_add_positive_numbers():  
assert add_numbers(1, 2) == 3  
  
@pytest.mark.end_to_end  
def test_add_negative_numbers():  
assert add_numbers(-1, -2) == -3  
  
@pytest.mark.skip  
def test_add_numbers_zero():  
assert add_numbers(0, 0) == 0  
  
class TestsUnit:  
@pytest.mark.unit  
def test_multiply_numbers(self):  
assert multiply_numbers(2, 3) == 6  
  
@pytest.mark.unit  
def test_multiply_numbers_zero(self):  
assert multiply_numbers(0, 0) == 0

To run all the tests from the root directory, you can use the following command:

pytest

The following output will be displayed:

You can add the -v flag to get more verbose output:

You can enable live console logging using the pytest -s command too. Our article on Pytest Logging covers how to write Pytest logs to console and files easily and even control the log level.

Run Tests in a Module

To run all tests in a specific file (module), use the following command:

pytest tests/unit/test_functions.py

Run Tests in a Directory

Perhaps you may decide to split your tests by unit, integration, end-to-end, performance, regression and so on.

In these cases it’s helpful to run tests within a specific directory, and you can use:

pytest tests/unit

This will find and run all tests in the unit directory. Similarly you can have directories containing integration, regression or performance tests.

Run Tests by Node IDs

To run a specific test, you can use the test’s node ID, which is essentially its path in the syntax filename.py::test_function_name.

For example, to run the test_add_negative_numbers function in the test_functions.py file, you can use the following command:

pytest tests/unit/test_functions.py::test_add_negative_numbers

You can find the node ID by running the tests with the -v flag.

Run Tests of a Specific Class

You can also run all tests in a specific class. To do this, you use the :: operator followed by the class name.

For example, to run all tests in the UnitTests class, you can use the following command:

pytest tests/unit/test_functions.py::TestsUnit

Run Tests by Marker Expressions:

Markers are a powerful tool that can be used to control the execution of your tests.

By using markers, you can run specific groups of tests, exclude tests, and prioritize tests. This can help you to write better tests and to get more value from your test suite.

In Pytest, you can assign markers to your test functions using the @pytest.mark decorator. You can then use these markers to run specific tests.

from operations.core import add_numbers, multiply_numbers  
import pytest  
  
def test_add_positive_numbers():  
    assert add_numbers(1, 2) == 3  
     
@pytest.mark.end_to_end  
def test_add_negative_numbers():  
    assert add_numbers(-1, -2) == -3  
  
@pytest.mark.skip  
def test_add_numbers_zero():  
    assert add_numbers(0, 0) == 0  
  
class TestsUnit:  
    @pytest.mark.unit  
    def test_multiply_numbers(self):  
        assert multiply_numbers(2, 3) == 6  
  
    @pytest.mark.unit  
    def test_multiply_numbers_zero(self):  
        assert multiply_numbers(0, 0) == 0
 

Markers can be easily defined like this in your pytest.ini file:

[pytest]
markers =
    unit : unit tests
    end_to_end  : end to end tests
    skip : slow tests

To run all tests with the unit marker, you can use the following command:

pytest -m unit

If You Want to Skip a Test

There may be situations where you want to skip a particular test.

@pytest.mark.skip

When pytest runs, it will see the @pytest.mark.skip line and know that it should skip this test.