Pytest

Install Pytest

1. Go to the Python Package tool window

2. Start typing pytest in the Search field of the Python Package tool window. Locate the package in the list of the available packages and click Install.

   

Create a test

1. Create a Python project.

2. In the main menu, go to File | New, choose Python file, type car.py, and click OK.

3. Copy and paste the Car class into the car.py file.

4. In the editor, place the caret at the brake method declaration.

5. Do one of the following:

   • Go to Navigate | Test.

   • From the context menu, choose Go To | Test.

     

   • Press Ctrl+Shift+T.

   PyCharm shows the list of available tests.

   

6. Click Create new test.

   The Create Test dialog opens.

   

   In the Create Test dialog, specify the following settings:

   • Target directory, where the new test class will be generated.

   • The name of the test file (in our example, test_car.py), and the name of the test class if needed.

   • Select the checkboxes next to the methods you want to include in the test class.

     Note that if you place the caret within a method, only this method name is included in the list. Also, mind the naming convention: the test method has the test prefix. The Run Test icon will appear in the editor gutter for all methods with such a prefix.

7. Click OK when ready. PyCharm generates the test file in the specified location.

8. PyCharm automatically generates a test file with the test method template. Replace the template code with the code that sets the initial speed value of Car to 50 and checks if speed gets properly set to 45 after the brake() function execution.

   from car import Car def test_car_brake(): car = Car(50) car.brake() assert car.speed == 45

Run a test

1. Click to run the test:

   

2. Note that PyCharm automatically creates a pytest Run/Debug configuration:

   

   Select Run pytest for test_car_pytest to execute the test.

3. Inspect test results:

   

4. Alter the assert statement to the following: assert my_car.speed == 4599.

5. Rerun the test to evaluate the assert failing report:

   

   Note that pytest provides an explicit report on the failure.

Debug a test

1. Set a breakpoint in the test, for example, on the car.brake() line of test_car_brake.

2. Click in the gutter next to the test and select Debug <test name>.

3. PyCharm runs the test in the debug mode and suspends it at the breakpoint. Inspect the variables in the Debug tool window and step through the code. For more information, refer to Examine suspended program.

Use fixtures

1. Modify your pytest test as follows:

   import pytest from car import Car @pytest.fixture def my_car(): return Car(50) def test_car_accelerate(my_car): my_car.accelerate() assert my_car.speed == 55 def test_car_brake(my_car): my_car.brake() assert my_car.speed == 45

   my_car() is a fixture function that creates a Car instance with the speed value equal to 50. It is used in test_car_accelerate and test_car_brake to verify correct execution of the corresponding functions in the Car class.

   Note that the my_car fixture is added to the code completion list along with other standard pytest fixtures, such as tempdir.

2. Click either of the icons, or run the entire test module.

Apply parametrization

1. let's create a set of speed values to test car.accelerate and car.brake functions: speed_data = {45, 50, 55, 100}

2. Modify the test code to the following:

   import pytest from car import Car speed_data = {45, 50, 55, 100} @pytest.mark.parametrize("speed_brake", speed_data) def test_car_brake(speed_brake): car = Car(50) car.brake() assert car.speed == speed_brake @pytest.mark.parametrize("speed_accelerate", speed_data) def test_car_accelerate(speed_accelerate): car = Car(50) car.accelerate() assert car.speed == speed_accelerate

   Note that PyCharm detects the newly created parameters and adds them to the completion list.

   

3. Run the test for the car.brake() function. You should expect the following test report:

   

You can also run the test for car.accelerate() function to ensure that it fails for all speed values but 55. For more information about parametrized test, refer to pytest documentation.