Fixes tests return values issue #1336

[evgueni-ovtchinnikov]

Changes in this pull request

Running SIRF tests produces a warning PytestReturnNotNoneWarning (pytest expects no return values) that will become an error in a future version of pytest. At the same time, currently returned values may be useful when running the tests manually. This PR covers both use cases.

Testing performed

Related issues

fixes #1336

Checklist before requesting a review

• I have performed a self-review of my code
• I have added docstrings/doxygen in line with the guidance in the developer guide
• I have implemented unit tests that cover any new or modified functionality
• The code builds and runs on my machine
• CHANGES.md has been updated with any functionality change

Contribution Notes

Please read and adhere to the contribution guidelines.

Please tick the following:

• The content of this Pull Request (the Contribution) is intentionally submitted for inclusion in SIRF (the Work) under the terms and conditions of the Apache-2.0 License.

[casperdcl]

would prefer we don't reinvent the wheel (#1331) but fine for now...