Unit testing and integration testing are critical for the successful continuous integration (CI) and delivery of any library belonging to the PyAnsys project.

In 1993, Kent Beck developed Test Driven Development (TDD) as part of the Extreme Programming software development process. TDD is the practice of writing unit tests before writing production code. The benefit of this practice is that you know each new line of code is working as soon as it is written. It’s easier to track down problems because only a small amount of code has been implemented since the execution of the last test. Furthermore, all test cases do not have to be implemented at once but rather gradually as the code evolves.

You should follow TDD when developing your PyAnsys project. Examples and best practices for unit tests follow.

Test framework#

For consistency, PyAnsys tools and libraries should use either the pytest or unittest framework for unit testing. The pytest framework is recommended unless a constraint in your project prevents you from using it. As described in Required files, you should place unit tests in The tests directory in the library’s root directory.

Add testing dependencies#

Requirements for testing dependencies should be included in The setup.py file, The pyproject.toml file, or a requirements_tests.txt file. Only pytest and pytest-cov must be specified as third-party dependencies because unittest is included in The Python Standard Library.

test = [
pytest = "*"
pytest-cov = "*"
        "test": ["pytest", "pytest-cov"],

You can use pip to install these testing dependencies:

python -m pip install .[test]
python -m pip install -r requirements_tests.txt

Organize test files#

You must place your test files in The tests directory. To guarantee that tests are run against the library source code, follow a src layout as explained in The src directory rather than having your Python library source located directly in the repository root directory.

This helps you to achieve these objectives:

  • Avoid testing the source of the repository rather than testing the installed package.

  • Catch errors caused by files that might be missed by the installer, including any C extensions or additional internal packages.

Test execution#

Once you have installed pytest, you can execute the test suite with this command:

pytest -v tests/

Filter tests#

To run a subset of all available tests, you can taking advantage of the keywords and markers flags:

Filter tests by keywords

pytest -k '<name pattern>'
pytest -k 'not <name pattern>'

Filter tests by markers

pytest -m slow

For more information about filtering tests, see Working with custom markers in the pytest documentation.

Testing methodology#

You should consider three levels of testing for your PyAnsys library: unit, integration, and functional.

  • Unit testing validates your library at the lowest possible level, isolating individual classes and methods without any communication with other libraries or services.

  • Integration testing validates that your library works in the context of an app or software stack. For example, if your library extends or wraps the features of an external service, you must test that service in conjunction with your library. On GitHub, the ideal approach for this would be to start your service using Docker and then test accordingly. You should still be testing at the individual class or method level, but you can now test how multiple libraries or services interact. This is mandatory for testing APIs and is preferred over mocking the service.

  • Functional testing should be used for validating workflows or long-running examples. Assume that you have a library that wraps a CAD service. You would validate that you can create complex geometry while directly interfacing with the service. Functional tests are great at discovering edge cases that are not normally found at the unit or integration level. However, functional testing should be limited to only a handful of examples because these tend to be long running and difficult to validate.

Each PyAnsys project should have all three levels of testing implemented in its testing framework. Consider implementing functional tests as examples within your project’s documentation examples. This lets you write helpful user-facing tests while accomplishing functional testing.

Unit testing#

Unit testing tests at the lowest possible level, isolated from other applications or libraries. For Python tool libraries like ansys-tools-protoc-helper, unit testing is sufficient to get high coverage (> 80%) of your library while actually testing the library.

These tests should be written to test a single method in isolation. For example, the following parse_chunks.py file has a method that deserializes chunks. The associated test_parse_chunks_py file tests this method in isolation.


This example assumes that you do not have a serialize_chunks function in your library. If you did, you could exclude it from the test_parse_chunks.py file.

def parse_chunks(chunks):
    """Deserialize gRPC chunks into a Numpy array.

    chunks : generator
        Generator from gRPC. Each chunk contains a bytes payload.

    dtype : np.dtype
        Numpy data type to interpret chunks as.

    array : np.ndarray
        Deserialized Numpy array.

    arrays = []
    for chunk in chunks:
        arrays.append(np.frombuffer(chunk.payload, ANSYS_VALUE_TYPE[chunk.value_type]))

     return np.hstack(arrays)
from ansys.api.mapdl.v0 import ansys_kernel_pb2 as anskernel
import numpy as np
import pytest

from ansys.mapdl.core.common_grpc import parse_chunks

DEFAULT_CHUNKSIZE = 256*1024  # 256 kB

def sample_array():
    """Generate a non-trivial (n x 3) float array."""
    sz = np.random.randint(100000, 200000)
    array = np.random.random((sz, 3)).astype(np.float64)
    assert array.nbytes > DEFAULT_CHUNKSIZE
    return array

def serialize_chunks(array):
    """Serialize an array into chunks."""
    # convert to raw
    raw = array.tobytes()
    value_type = 5  # float64

    i = 0
    while True:
        piece = raw[i:i + DEFAULT_CHUNKSIZE]
        length = len(piece)
        if length == 0:
        yield anskernel.Chunk(payload=piece, size=length, value_type=value_type)

def test_deserialize_chunks(sample_array):
    parsed_array = parse_chunks(serialize_chunks(sample_array))
    parsed_array = parsed_array.reshape(-1, 3)
    assert np.allclose(sample_array, parsed_array)

Integration testing#

This section explains Wrapped service methods and how to Test using remote method invocation.

Wrapped service methods#

Any PyAnsys library that provides features by wrapping a gRPC interface should include tests of the gRPC methods exposed by the PROTO files and wrapped by the Python library. They would not be expected to test the features of the server but rather the APIs exposed by the server. For example, if testing the GetNode gRPC method, then your integration test would test the wrapped Python function. If the Python library wraps this gRPC method with a get_node method, your test would be implemented within the tests/test_nodes.py file.

 message Node
   int32      id = 1;
   double     x = 2;
   double     y = 3;
   double     z = 4;

 message NodeRequest {
   int32      num = 1;

 message NodeResponse {
   Node       node = 1;

service SomeService {

   rpc GetNode(NodeRequest)  returns (NodeResponse);
   // other methods
from ansys.product.service.v0 import service_pb2

def get_node(self, index):
    """Get the coordinates of a node for a given index.

    index : int
        Index of the node.

        Coordinates of the node.

    >>> from ansys.product.service import SomeService
    >>> srv = SomeService()
    >>> srv.create_node(1, 4.5, 9.0, 3.2)
    >>> node = srv.get_node(1)
    >>> node
    (4.5, 9.0, 3.2)

    resp = service_pb2.GetNode(index=index)
    return resp.x, resp.y, resp.z
def test_get_node(srv):

    node_index = 1
    node_coord = 0, 10, 20
    srv.create_node(node_index, node_coord*)
    assert srv.get_node(node_index) == node_coord

The goal of the unit test should be to test the API rather than the product or service. The GetNode gRPC method should have already been tested when designing and developing the service.

Test using remote method invocation#

For a Remote Method Invocation (RMI)-like method, it is only necessary to test the method with a basic case and potentially with any edge cases. A RMI-like API might send and receive strings that are executed on the server using a custom API or language only available within the context of the service.

For example, if a method has a RMI service definition named SendCommand() and a Python wrapping named send_command, your code and the example test would look like this:

message SendCommand()
def send_command(command):
    """Run a command on the remote server.

    command : str
        Command to run on the remote server.
def test_send_command(srv):
    output = srv.send_command("CREATE,1")
    assert "Created 1" in output

Note that this test only validates that the "CREATE,1" command has been received, executed, and sent back to the client. It does not validate all commands. Running such a test is necessary only if there are edge cases, which include characters that cannot be streamed or use long-running commands.

Functional testing#

Functional testing should test the Python library using scripts or examples that are expected to be executed by the user. Unlike unit or integration testing, functional tests are testing the library as a whole by calling several methods to accomplish a task. You should run these tests only after unit and integration testing is complete. Ideally, you should run them outside the pytest framework while building documentation with Sphinx-Gallery.


Functional tests should not contribute to global library coverage. Testing should always be done on individual functions or methods.

Test code coverage#

Because Python is an interpreted language, syntax errors can only be caught during the almost trivial compile times. Thus, developers of Python libraries should aim to have high coverage for their libraries. Coverage is defined as parts of the executable and usable source that are tested by unit tests. You can use the pytest-cov library to view the coverage for your library.

Configure code coverage#

If you do not configure code coverage properly, the resulting report does not show the real scope covered by the test suite.

Assuming that a PyAnsys project follows The src directory layout, you must pass the following flag when executing tests:

pytest --cov=ansys.<product>.<library> --cov-report=term tests/

This command tells pytest-cov to look for source code in the src/ansys/<product> directory and generate a terminal report for all tests located in The tests directory.

While 100% coverage is ideal, the law of diminishing returns applies to the coverage of a Python library. Consequently, achieving 80-90% coverage is often sufficient. For parts of your library that are difficult or impossible to test, consider using # pragma: no cover at the end of the method definition, branch, or line to denote that part of the code cannot be reasonably tested. For example, if part of your module performs a simple import test of matplotlib and raises an error when the library is not installed, it is not reasonable to attempt to test this and assume full coverage:

    import matplotlib
except ImportError:  # pragma: no cover
    raise ImportError("Install matplotlib to use this feature.")

You should only avoid coverage of parts of your library where you cannot reasonably test without an extensive testing suite or setup. Most methods and classes, including edge cases, can be reasonably tested. Even parts of your code that raise errors like TypeError or ValueError when users input the wrong data type or value can be reasonably tested.

Enforce code coverage#

One way of enforcing unit test coverage with a project on GitHub is to use codecov.io to enforce minimum patch (and optionally project) coverage. Because this app is already available to the Ansys GitHub organization, you can simply add a codecov.yml file to the root directory of your repository. This example file provides a sample configuration:

  layout: "diff"
  behavior: default

        # basic
        # target: 50%
        threshold: 0%
        # advanced
        if_not_found: success
        if_ci_failed: error
        if_no_uploads: error
        # basic
        target: 90%
        if_not_found: success
        if_ci_failed: error
        if_no_uploads: error

Using a codecov.yml file requires that each PR has a patch coverage of 90%, meaning that 90% of any source added to the repository (unless ignored) must be covered by unit tests.

Test using GitHub Actions#

Effective CI/CD assumes that unit testing is developed during feature development or bug fixes. However, given the limited scope of the local development environment, it is often not possible to enforce testing on multiple platforms, or even to enforce unit testing in general. However, with the proper automated CI/CD, such testing can still occur and be enforced automatically.

GitHub Actions is the preferred automated CI/CD platform for running Python library unit tests for PyAnsys. It can be used immediately by cloning the project template.

  name: "Test library"
  runs-on: ${{ matrix.os }}
         os: [ubuntu-latest, windows-latest]
         python-version: ['3.9', '3.10', '3.11', '3.12']
    - name: "Run pytest"
      uses: ansys/actions/tests-pytest@v4
        python-version: ${{ matrix.python-version }}
        pytest-markers: "-k 'mocked'"
        pytest-extra-args: "--cov=ansys.<library> --cov-report=term --cov-report=xml:.cov/coverage.xml --cov-report=html:.cov/html"

    - name: "Upload coverage results"
      uses: actions/upload-artifact@v4
      if: matrix.python-version == ${{ env.MAIN_PYTHON_VERSION }}
        name: coverage-html
        path: .cov/html
        retention-days: 7