Taming Nondeterminism with Dependency Injection

Take back control of your code!

Haki Benita

Development Programming Software Design Testing

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There are many sources of nondeterminism in code such randomness, IO, environment variables, databases and many more. Nondeterminism is a source of confusion, and it makes testing difficult. One way to control nondeterminism is using the dependency injection pattern.

In this talk I'll guide the audience through a series of problems that demonstrate how nondeterminism can pose incredible challenges even in simple code. Tackling one problem after another, I gradually integrate dependency injection into the code to address these challenges!

A rough outline of the talk:

- Present a problem that involves nondeterminism (test a function that returns tomorrow's date)
- Attempt to test in conventional ways (`datetime` cannot be mocked without external packages...)
- Offer solution (Inject literal values... show how simple it is to test)
- Present a function that requires more than a literal (a function the requires the current time more than once)
- Demonstrate injection of functions and services (Using nominal typing, e.g using ABC)
- Present the dependency injection pattern
- Replace AC with structural subtyping (Using`typing_extensions.Protocol`)
- Conclusion

After watching this talk, I expect my audience to learn and understand the following:

- The challenges nondeterminism poses
- How to identify nondeterminism in code
- What dependency injection is, and how it addresses challenge related to nondeterminism
- How to implement and integrate dependency injection into Python code

Type: Talk (30 mins); Python level: Intermediate; Domain level: Intermediate


Haki Benita

Haki Benita

Haki is a software developer and a technical lead. He takes special interest in databases, web development, software design and performance tuning. Haki also writes about development and performance in his blog hakibenita.com.