Test Anti-Pattern Detection
Quick, pragmatic analysis of.NET test code for anti-patterns and quality issues that undermine test reliability, maintainability, and diagnostic value.
When to Use
- User asks to review test quality or find test smells
- User wants to know why tests are flaky or unreliable
- User asks "are my tests good?" or "what's wrong with my tests?"
- User requests a test audit or test code review
- User wants to improve existing test code
When Not to Use
- User wants to write new tests from scratch (use
writing-mstest-tests) - User wants direct implementation fixes in MSTest code rather than a diagnostic review (use
writing-mstest-tests) - User asks to fix swapped
Assert.AreEqualargument order (usewriting-mstest-tests) - User asks to convert
DynamicDatafromIEnumerable<object[]>toValueTuple(usewriting-mstest-tests) - User wants to run or execute tests (use
run-tests) - User wants to migrate between test frameworks or versions (use migration skills)
- User wants to measure code coverage (out of scope)
- User wants a deep formal test smell audit with academic taxonomy and extended catalog (use
exp-test-smell-detection)
Inputs
| Input | Required | Description |
|---|---|---|
| Test code | Yes | One or more test files or classes to analyze |
| Production code | No | The code under test, for context on what tests should verify |
| Specific concern | No | A focused area like "flakiness" or "naming" to narrow the review |
Workflow
Step 1: Gather the test code
Read the test files the user wants reviewed. If the user points to a directory or project, scan for all test files using the framework-specific markers in the dotnet-test-frameworks skill (e.g., [TestClass], [Fact], [Test]).
If production code is available, read it too -- this is critical for detecting tests that are coupled to implementation details rather than behavior.
Step 2: Scan for anti-patterns
Check each test file against the anti-pattern catalog below. Report findings grouped by severity.
Critical -- Tests that give false confidence
| Anti-Pattern | What to Look For |
|---|---|
| No assertions | Test methods that execute code but never assert anything. A passing test without assertions proves nothing. |
| Swallowed exceptions | try {...} catch {} or catch (Exception) without rethrowing or asserting. Failures are silently hidden. |
| Assert in catch block only | try {Act();} catch (Exception ex) {Assert.Fail(ex.Message);} -- use Assert.ThrowsException or equivalent instead. The test passes when no exception is thrown even if the result is wrong. |
| Always-true assertions | Assert.IsTrue(true), Assert.AreEqual(x, x), or conditions that can never fail. |
| Commented-out assertions | Assertions that were disabled but the test still runs, giving the illusion of coverage. |
High -- Tests likely to cause pain
| Anti-Pattern | What to Look For |
|---|---|
| Flakiness indicators | Thread.Sleep(...), Task.Delay(...) for synchronization, DateTime.Now/DateTime.UtcNow without abstraction, Random without a seed, environment-dependent paths. |
| Test ordering dependency | Static mutable fields modified across tests, [TestInitialize] that doesn't fully reset state, tests that fail when run individually but pass in suite (or vice versa). |
| Over-mocking | More mock setup lines than actual test logic. Verifying exact call sequences on mocks rather than outcomes. Mocking types the test owns. For a deep mock audit, use exp-mock-usage-analysis. |
| Implementation coupling | Testing private methods via reflection, asserting on internal state, verifying exact method call counts on collaborators instead of observable behavior. |
| Broad exception assertions | Assert.ThrowsException<Exception>(...) instead of the specific exception type. Also: [ExpectedException(typeof(Exception))]. |
Medium -- Maintainability and clarity issues
| Anti-Pattern | What to Look For |
|---|---|
| Poor naming | Test names like Test1, TestMethod, names that don't describe the scenario or expected outcome. Good: Add_NegativeNumber_ThrowsArgumentException. |
| Magic values | Unexplained numbers or strings in arrange/assert: Assert.AreEqual(42, result) -- what does 42 mean? |
| Duplicate tests | Three or more test methods with near-identical bodies that differ only in a single input value. Should be data-driven ([DataRow], [Theory], [TestCase]). For a detailed duplication analysis, use exp-test-maintainability. Note: Two tests covering distinct boundary conditions (e.g., zero vs. negative) are NOT duplicates -- separate tests for different edge cases provide clearer failure diagnostics and are a valid practice. |
| Giant tests | Test methods exceeding ~30 lines or testing multiple behaviors at once. Hard to diagnose when they fail. |
| Assertion messages that repeat the assertion | Assert.AreEqual(expected, actual, "Expected and actual are not equal") adds no information. Messages should describe the business meaning. |
| Missing AAA separation | Arrange, Act, Assert phases are interleaved or indistinguishable. |
Low -- Style and hygiene
| Anti-Pattern | What to Look For |
|---|---|
| Unused test infrastructure | [TestInitialize]/[SetUp] that does nothing, test helper methods that are never called. |
| IDisposable not disposed | Test creates HttpClient, Stream, or other disposable objects without using or cleanup. |
| Console.WriteLine debugging | Leftover Console.WriteLine or Debug.WriteLine statements used during test development. |
| Inconsistent naming convention | Mix of naming styles in the same test class (e.g., some use Method_Scenario_Expected, others use ShouldDoSomething). |
Step 3: Calibrate severity honestly
Before reporting, re-check each finding against these severity rules:
- Critical/High: Only for issues that cause tests to give false confidence or be unreliable. A test that always passes regardless of correctness is Critical. Flaky shared state is High.
- Medium: Only for issues that actively harm maintainability -- 5+ nearly-identical tests, truly meaningless names like
Test1. - Low: Cosmetic naming mismatches, minor style preferences, assertion messages that could be better. When in doubt, rate Low.
- Not an issue: Separate tests for distinct boundary conditions (zero vs. negative vs. null). Explicit per-test setup instead of
[TestInitialize](this *improves* isolation). Tests that are short and clear but could theoretically be consolidated.
IMPORTANT: If the tests are well-written, say so clearly up front. Do not inflate severity to justify the review. A review that finds zero Critical/High issues and only minor Low suggestions is a valid and valuable outcome. Lead with what the tests do well.
Step 4: Report findings
Present findings in this structure:
- Summary -- Total issues found, broken down by severity (Critical / High / Medium / Low). If tests are well-written, lead with that assessment.
- Critical and High findings -- List each with:
- The anti-pattern name - The specific location (file, method name, line) - A brief explanation of why it's a problem - A concrete fix (show before/after code when helpful)
- Medium and Low findings -- Summarize in a table unless the user wants full detail
- Positive observations -- Call out things the tests do well (sealed class, specific exception types, data-driven tests, clear AAA structure, proper use of fakes, good naming). Don't only report negatives.
Step 5: Prioritize recommendations
If there are many findings, recommend which to fix first:
- Critical -- Fix immediately, these tests may be giving false confidence
- High -- Fix soon, these cause flakiness or maintenance burden
- Medium/Low -- Fix opportunistically during related edits
Validation
- Every finding includes a specific location (not just a general warning)
- Every Critical/High finding includes a concrete fix
- Report covers all categories (assertions, isolation, naming, structure)
- Positive observations are included alongside problems
- Recommendations are prioritized by severity
Common Pitfalls
| Pitfall | Solution |
|---|---|
| Reporting style issues as critical | Naming and formatting are Medium/Low, never Critical |
| Suggesting rewrites instead of targeted fixes | Show minimal diffs -- change the assertion, not the whole test |
| Flagging intentional design choices | If Thread.Sleep is in an integration test testing actual timing, that's not an anti-pattern. Consider context. |
| Inventing false positives on clean code | If tests follow best practices, say so. A review finding "0 Critical, 0 High, 1 Low" is perfectly valid. Don't inflate findings to justify the review. |
| Flagging separate boundary tests as duplicates | Two tests for zero and negative inputs test different edge cases. Only flag as duplicates when 3+ tests have truly identical bodies differing by a single value. |
| Rating cosmetic issues as Medium | Naming mismatches (e.g., method name says ArgumentException but asserts ArgumentOutOfRangeException) are Low, not Medium -- the test still works correctly. |
| Ignoring the test framework | xUnit uses [Fact]/[Theory], NUnit uses [Test]/[TestCase], MSTest uses [TestMethod]/[DataRow] -- use correct terminology |
| Missing the forest for the trees | If 80% of tests have no assertions, lead with that systemic issue rather than listing every instance |