Programming in C# with Unit Testing — Lesson 3: Mocks, Stubs, Dependency Isolation and Refactoring

Learning Objectives

• Use mocks, stubs, fakes, spies, interfaces, adapters, and controlled dependencies without over-mocking
• Refactor legacy code, isolate seams, remove duplication, improve readability, and preserve behavior through tests
• Validate mocks, stubs, dependency isolation and refactoring decisions with documented requirements, evidence, risk controls, and measurable acceptance criteria

Detailed Topics

• Use mocks: Use mocks, stubs, fakes, spies, interfaces, adapters, and controlled dependencies without over-mocking
• Refactor legacy code: Refactor legacy code, isolate seams, remove duplication, improve readability, and preserve behavior through tests
• Validate mocks: Validate mocks, stubs, dependency isolation and refactoring decisions with documented requirements, evidence, risk controls, and measurable acceptance criteria

Guided Demonstration

1. Review the requirement, users, data, dependencies, permissions, risks, and expected result.
2. Demonstrate the relevant configuration, development, analysis, administration, testing, or operational workflow step by step.
3. Capture settings, outputs, logs, screenshots, calculations, test results, and other useful evidence.
4. Compare the observed result with acceptance criteria and explain any corrective action.

Hands-On Activity

Analyze a realistic business case, compare implementation options, and validate the selected approach.

• Document assumptions, prerequisites, and the planned sequence before starting.
• Complete the activity and preserve evidence of normal, boundary, and failure behavior.
• Record issues, corrective actions, reusable notes, and the next improvement priority.

Scenario Analysis

• Identify the business or technical decision that must be made.
• Compare valid implementation approaches and their trade-offs.
• Consider security, privacy, accessibility, performance, support, and operational impact.

Troubleshooting Focus

• Separate symptoms from causes and collect evidence before applying a fix.
• Check configuration, data, permissions, dependencies, capacity, connectivity, and recent changes.
• Validate rollback, recovery, ownership, user impact, and business continuity.

Validation Checklist

• The requirement, scope, inputs, and expected outcome are clear.
• The selected design or configuration is documented and follows approved standards.
• Normal, boundary, failure, security, accessibility, and operational conditions are reviewed.
• The result is supported by evidence and the next improvement is prioritized.

Lesson Outcome

Learners can explain and apply Mocks, Stubs, Dependency Isolation and Refactoring in a realistic scenario and validate the result with documented evidence.