• Testing scientific software is highly important,
  as it has direct impact on scientific insight.
• The largest part of scientific software is not thoroughly tested or even not tested at all.
• Tests can only prove the existence of bugs, not their absence.
• Testing should be done as early as possible, as often as possible, and as automatic as possible.
• Test automatisation has dramatic impact on the design of the code to be tested (e.g., modularity).
• Test-driven development turns the usual sequence upside down and leads to high test coverage.
• High test coverage by automatic tests increases the trust in software.
• Test-driven development leads to tests documenting the code and its specifications.

Python Unittest Module
Unit testing framework originally inspired by JUnit