exp-test-maintainability

name	exp-test-maintainability
description	Detects duplicate boilerplate, copy-paste tests, and structural maintainability issues across .NET test suites. Use when the user asks to reduce repetition, consolidate similar test methods, convert copy-paste tests to data-driven parameterized tests, suggest a better test structure, or identify refactoring opportunities. Identifies repeated construction, assertion patterns, copy-paste methods convertible to DataRow/Theory/TestCase, redundant setup/teardown, and shared infrastructure. Produces an analysis report with concrete before/after suggestions. Works with MSTest, xUnit, NUnit, and TUnit. DO NOT USE FOR: writing new tests (use writing-mstest-tests), reviewing test quality or anti-patterns (use test-anti-patterns), or deep mock auditing (use exp-mock-usage-analysis).
license	MIT

Test Maintainability Assessment

Analyze .NET test code for maintainability issues: duplicated boilerplate, copy-paste test methods, and structural repetition across test methods and classes. Produce a report of refactoring opportunities with concrete before/after suggestions. The goal is analysis only — do not modify any files.

When to Use

• User asks to find duplicated code or boilerplate in tests
• User wants to know where test code can be DRY-ed up
• User asks to reduce test duplication, improve test readability, or clean up test boilerplate
• User asks for refactoring opportunities in a test suite
• User wants to identify shared setup or teardown candidates
• User asks "what patterns repeat across my tests?"
• User wants to centralize test data, introduce builders or helpers

When Not to Use

• User wants to write new tests from scratch (use writing-mstest-tests)
• User wants to detect anti-patterns or code smells (use test-anti-patterns)
• User wants to actually perform the refactoring (help them directly, this skill only analyzes)

Inputs

Input	Required	Description
Test code	Yes	One or more test files or a test project directory to analyze
Production code	No	The code under test, for context on what abstractions might help
Scope	No	Whether to analyze within a single class or across multiple classes

Workflow

Step 1: Gather the test code

Read all test files the user provides or references. If the user points to a directory or project, scan for all test files using these framework markers:

Framework	Test class markers	Test method markers
MSTest	[TestClass]	[TestMethod], [DataTestMethod]
xUnit	(none — convention-based)	[Fact], [Theory]
NUnit	[TestFixture]	[Test], [TestCase], [TestCaseSource]
TUnit	(none — convention-based)	[Test]

Step 2: Identify maintainability issues

Scan for these categories:

Category 1: Repeated object construction

Look for the same object being constructed in 3+ test methods with identical or near-identical parameters.

Indicators:

• new ClassName(...) appearing with identical arguments in multiple tests
• Multiple tests creating the same "system under test" with similar configuration
• Repeated mock/fake/stub creation with the same setup

Potential refactorings:

• Extract a factory method or test helper (e.g., CreateSut(), CreateDefaultOrder())
• Use [TestInitialize]/constructor/[SetUp] for shared construction
• Introduce a builder pattern for complex objects with many variations

Example — before:

[TestMethod]
public void Process_ValidOrder_Succeeds()
{
    var logger = new FakeLogger();
    var email = new FakeEmailService();
    var inventory = new FakeInventory(stock: 100);
    var processor = new OrderProcessor(logger, email, inventory);
    // ...
}

[TestMethod]
public void Process_EmptyItems_Fails()
{
    var logger = new FakeLogger();
    var email = new FakeEmailService();
    var inventory = new FakeInventory(stock: 100);
    var processor = new OrderProcessor(logger, email, inventory);
    // ...
}

After — extract factory:

private static OrderProcessor CreateProcessor(int stock = 100)
{
    return new OrderProcessor(new FakeLogger(), new FakeEmailService(), new FakeInventory(stock));
}

Category 2: Repeated assertion patterns

Look for the same sequence of assertions appearing in 3+ test methods.

Indicators:

• Multiple tests asserting the same set of properties on a result object
• Repeated null-check-then-value-check sequences
• Same collection of Assert.AreEqual calls across methods

Potential refactorings:

• Extract a custom assertion helper (e.g., AssertValidOrder(order, expectedTotal, expectedStatus))
• Use framework-specific assertion extensions
• Introduce a Verify method that checks a standard set of properties

Category 3: Copy-paste test methods

Look for test methods with near-identical bodies differing only in input values or a single parameter.

Indicators:

• 3+ methods with the same structure but different literal values
• Methods that could be collapsed into [DataRow]/[Theory]/[TestCase]
• Test names that follow a pattern like Method_Input1_Result, Method_Input2_Result

Potential refactorings:

• Convert to parameterized tests with [DataRow]/[InlineData]/[TestCase]
• Use [DynamicData]/[MemberData]/[TestCaseSource] for complex inputs
• Prefer [DataRow] with DisplayName over [DynamicData] when all values are compile-time constants. Reserve [DynamicData] for computed or complex values.
• Add DisplayName for non-obvious parameter values. [DataRow("Gold", 100.0, 90.0)] is self-explanatory; [DataRow(3, 7, 42)] is not.

Category 4: Duplicated setup/teardown logic

Look for initialization or cleanup code repeated across test classes.

Indicators:

• Multiple [TestInitialize]/[SetUp] methods with similar bodies
• Repeated database seeding, file creation, or HTTP client configuration
• Same using/IDisposable cleanup pattern across classes

Potential refactorings:

• Extract a shared test base class or fixture
• Use composition with a shared helper class
• Create a test context factory

Category 5: Repeated test infrastructure

Look for structural patterns shared across test classes.

Indicators:

• Same mock interfaces configured identically in multiple classes
• Repeated HttpClient setup with similar DelegatingHandler patterns
• Same logging/configuration scaffolding across test classes

Potential refactorings:

• Extract a shared test fixture or helper library
• Create reusable fake implementations
• Introduce a test harness class

Step 3: Apply calibration rules

Before reporting, filter findings through these rules:

• Only report at 3+ occurrences. Two similar setups are not boilerplate — they may be intentional clarity.
• Don't flag simple constructors. new Calculator() or new List<int>() is not meaningful boilerplate. Don't recommend builders for new User(1, "Alice") either.
• Respect intentional verbosity. If each test is self-contained and reads clearly on its own, explicit setup per test is a valid choice. Note it but don't flag it as a problem.
• Distinguish structural similarity from true duplication. Tests that follow AAA (Arrange-Act-Assert) will look similar by nature. Only flag when the actual code (not just the structure) is duplicated.
• Consider the blast radius of refactoring. A helper shared across 20 tests creates coupling. Note the trade-off.
• If tests are already well-maintained, say so. A report finding only minor opportunities is perfectly valid. Acknowledge what's already good.

Step 4: Report findings

Present findings in this structure:

1. Summary — How many patterns found, broken down by category. If the test suite is clean, lead with that.
2. Findings by category — For each pattern found:
   • Category name and description
   • Locations: list the specific test methods and files involved
   • The duplicated code pattern (show a representative sample)
   • Suggested refactoring with a concrete before/after example
   • Estimated impact: how many lines/methods would be simplified
3. Refactoring priority — Rank findings by:
   • Occurrence count (more occurrences = higher value)
   • Complexity of the duplicated code (complex setup > simple construction)
   • Risk (low-risk extractions first)
4. Trade-offs — For each suggestion, note:
   • What readability is gained
   • What locality/independence is lost
   • Whether it's worth it given the occurrence count

Validation

• Every finding includes specific file and method locations
• Every finding shows the actual duplicated code, not just a description
• Every suggestion includes a concrete before/after example
• Findings are filtered through the 3+ occurrence threshold
• Simple constructors are not flagged
• Trade-offs are acknowledged for each suggestion
• If tests are clean, the report says so upfront

Common Pitfalls

Pitfall	Solution
Flagging AAA structure as duplication	The Arrange-Act-Assert pattern is not boilerplate — flag only when the actual code repeats
Suggesting extraction for 2 occurrences	Wait for 3+ before recommending extraction
Recommending base classes for everything	Prefer composition (helpers, factories) over inheritance
Ignoring the readability cost	Every extraction adds indirection — note the trade-off
Flagging simple new X() as boilerplate	Only flag complex construction with multiple parameters or configuration
Recommending DRY at the expense of test isolation	Tests that share mutable state through helpers become coupled — warn about this