Private dependency

Q: How deeply does Unit Testing Principles, Practices, and Patterns cover private dependency?

Defines private dependencies, distinguishes mutable and immutable forms, and contrasts classical and London treatment.

As explained in Unit Testing Principles, Practices, and Patterns

A dependency that is not shared between tests and therefore cannot transmit state between their executions.

A private dependency is not shared between tests, so its state cannot transmit interference between their executions. A test may create and reuse its own instance without making that dependency shared. section 2.1

Classify private dependencies by whether their state can change:

An immutable private dependency is a value object; equivalent instances can be used interchangeably. section 2.2
A mutable private dependency can change during a test but remains private when tests do not reuse the same instance. section 2.2 section 2.1

Private dependencies do not require replacement merely to isolate tests. The classical approach keeps them intact, while the London approach replaces mutable private dependencies as well as shared ones; immutable dependencies remain intact. section 2.2

Store and Product

A Store created inside each purchase test is a mutable private dependency. Product.Shampoo is an immutable private dependency, or value object. A database reused by tests is shared instead, because its state can affect other tests. section 2.2 section 2.1

How Unit Testing Principles, Practices, and Patterns covers it

Cover of Unit Testing Principles, Practices, and Patterns

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Related concepts

value objectincludes · A value object is an object whose meaning and equality derive from its attribute values rather than an independent identity, typically with immutable state.
out-of-process dependencycontrasts with · An out-of-process dependency is a dependency that runs outside the application's execution process and provides access to data or services external to in-memory execution.
shared dependencycontrasts with · A shared dependency is a dependency whose internal state is reused or accessible across multiple tests.

This explainer was generated by Manning's knowledge graph from the text of Unit Testing Principles, Practices, and Patterns. The section links point to the parts of the book it draws on.