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“Don’t Mock What You Don’t Own” in 5 Minutes

Hynek Schlawack · 21 Jun 2022

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Hynek Schlawack did not write this page.

Every claim below was made in this piece, quoted word for word and numbered in the order the piece makes them, so you can read it there rather than take our word for it. The sentence above each quote is our reading of the claim, not their wording. Each quote was checked against a stored copy of the page at build time; where the two differ, the quote is the fact.

  1. Our reading

    The principle 'Don't Mock What You Don't Own' means that mock objects should be used to substitute one's own objects rather than third-party ones.

    Their wordsThe principle Don't Mock What You Don't Own means that whenever you employ mock objects, you should use them to substitute your own objects and not third-party ones2.

  2. Our reading

    Using nested mocks to mimic third-party APIs can make tests brittle, unidiomatic, and difficult to debug.

    Their wordsThis is a business logic test and the purpose of the test is drowning in boilerplate necessary to mimic the API of an HTTP client that can change at any time. That makes the test brittle and unidiomatic.

  3. Our reading

    To keep business code testable and idiomatic, one should avoid directly using third-party dependencies in it.

    Their wordsCorollary: To keep your business code testable and idiomatic, avoid directly using third-party dependencies in it.

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