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Claude Code in Your Development Flow

Lesson 4: Test Generation and Code Review with Claude Code

Lesson Objectives

By the end of this lesson, students should be able to:

  • Write test generation prompts that produce behavior-focused tests
  • Apply the edge-case specification technique for comprehensive test coverage
  • Use Claude Code for focused, scoped code reviews
  • Integrate Claude Code into a pre-commit review habit

Lesson Content

Behavior-focused test generation.

The default Claude Code test generation output tests implementation details – what internal functions are called, what exact return structure is produced. These tests break on refactoring even when behavior is preserved. Behavior-focused tests survive refactoring because they test inputs and expected outputs.

Request pattern for behavior-focused tests: “ Write tests for processOrder()` that:

  • Test the function's observable behavior (inputs and expected outputs)
  • Do not assert on internal implementation details
  • Cover these cases: valid order, empty cart, negative quantity, unavailable item, payment failure
  • Use [team's test framework] and [team's assertion style from CLAUDE.md]

“`

The explicit case list in the request is the key element – it forces test coverage of the edge cases you specify rather than the happy path Claude defaults to.

The edge-case specification technique.

Before asking for test generation, ask Claude to identify edge cases:

  1. "What are the edge cases and boundary conditions for this function?"
  2. Review Claude's list – add any your domain knowledge surfaces that Claude missed
  3. Pass the complete list as the coverage specification for test generation

This two-step pattern produces more comprehensive tests than one-step generation because it forces explicit edge case identification before writing the tests.

Scoped code review.

The most useful Claude Code review requests are specific:

  • Security review: "Review src/auth/ for authentication vulnerabilities – specifically session management, token validation, and input sanitization"
  • Performance review: "Review this database query and the data it operates on for N+1 query patterns"
  • Style review: "Review this PR diff for adherence to the conventions in CLAUDE.md"
  • Logic review: "Review this function for unhandled edge cases – specifically null inputs, empty collections, and integer overflow"

Each scoped review produces findings in a specific domain. Generic "review this code" produces a surface-level observation that requires more follow-up.

The pre-commit review habit.

A two-minute pre-commit Claude Code review habit:

  1. git diff --staged to see what you are about to commit
  2. Share the diff with Claude: "Review this diff for obvious issues before I commit"
  3. Address any findings, then commit

Not every pre-commit review finds something. But the ones that do – catching a missing error handler, an unvalidated input, an off-by-one – are worth the two minutes every time.

Practical Example

A developer writes a payment processing function and asks Claude Code to generate tests.

First request (generic): Claude generates ten tests that all pass – but seven test internal method calls rather than actual payment outcomes.

Second request (behavior-focused with explicit cases): she specifies fourteen behavioral cases including all error paths.

Claude generates fourteen tests covering each case.

Two of the generated tests fail – surfacing actual bugs in the payment function before they reach staging.

The behavior specification, not the generation, was the quality-determining step.

Safety Notes

When using Claude Code for security-focused code reviews, treat Claude's findings as a first pass, not a comprehensive security audit. AI-assisted review catches common vulnerability patterns well. It does not replace penetration testing, formal security review, or domain-specific security expertise for high-risk applications. Use Claude's security review findings to catch low-hanging-fruit issues before engaging a security specialist.

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