Testability

Kind: quality-attribute

Layer: Computation Core

Record: architecture:testability

Severity: mandatory

Scope: class, module, service

Canonical: Ontology

The degree to which code can be tested in isolation, with its dependencies, time and randomness supplied by the test.

Listed in Architecture principles, after Static Analysis and before Validation.

Requires

• Low Coupling
• Deterministic Behavior

Reinforces

• Dependency Inversion Principle (DIP)
• Pure Functions

Enables

• Regression Safety

Conflicts with

• Hidden Dependency
• Test Pyramid Inversion

In tension with

• Encapsulation Extremes
• Singleton Pattern
• Service Locator Pattern
• Singleton Pattern / Testability
• Service Locator Pattern / Testability

Tensions

• Testability / Encapsulation Extremes

Violated by

• Hidden Time/Randomness/Global State
• Hidden Dependency

Refactored by

• Dependency Injection
• Make Effects Explicit

Severity

• mandatory

Category

• Correctness / Determinism / Verification

Enforced by

• rules/eslint/no-test-without-subject.eslint.rule.ts

Reinforced by

• Interface-Based Design
• Referential Transparency
• Single Responsibility Principle
• Stateless Processing
• Ports and Adapters Architecture
• Clean Architecture
• Controlled Side Effects

Enabled by

• Postconditions
• High Cohesion
• State Isolation

Linked from

• The check comes first
• Computation and resource
• Scale follows determinism
• Anti-patterns
• Contracts / Interfaces / Compatibility
• Correctness / Determinism / Verification
• Core Modular Design
• SOLID / Object-Oriented Design
• Creational Patterns
• Scalability / Performance / Optimization
• Streaming / Pipeline / Dataflow Processing
• Plugin / Extensibility / IoC
• Codebase / System Architecture Styles
• Transactions / State / Concurrency
• Causality / Ordering / Distributed Time
• Correctness / Determinism / Verification
• Severity levels
• The resolutions