Test Anti Patterns

---
name: test-anti-patterns
description: >
  Detection-focused review of .NET test code for anti-patterns that
  undermine reliability and diagnostic value.
  USE FOR: audit test quality, review test code, find test anti-patterns,
  tests pass but don't verify anything, flaky tests, ordering dependency,
  duplicate tests, magic values, missing/no assertions, swallowed
  exceptions, always-true assertions, over-mocking, test coupling, coverage
  touching, coverage inflation.
  DO NOT USE FOR: writing new tests (use writing-mstest-tests), direct
  MSTest API rewrites or implementation-only fixes such as swapped
  Assert.AreEqual argument order, running tests (use run-tests), migrating
  between frameworks (use migration skills), deep formal audit based on
  academic test smell taxonomy (use test-smell-detection).
license: MIT
---

# 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.AreEqual` argument order (use `writing-mstest-tests`)
- User asks to convert `DynamicData` from `IEnumerable<object[]>` to `ValueTuple` (use `writing-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 `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. |
| **Coverage touching** | Test class that methodically calls every public method on a type — often in alphabetical or declaration order — without asserting meaningful outcomes. Each test typically does `var result = sut.MethodName(...)` with no assertion, or only a trivial `Assert.IsNotNull(result)`. The intent is to inflate code-coverage metrics rather than verify behavior. Distinct from a single assertion-free test: the pattern is *systematic* coverage of the surface area with no real verification. |
| **Self-referential assertion** | Asserts that the output of an operation equals its input when the operation is expected to be an identity or no-op, e.g. `Assert.AreEqual(input, Parse(input.ToString()))` or `Assert.AreEqual(x, Identity(x))`. The test is tautological — it can only fail if the round-trip is broken, but it never verifies that a *transformation* actually happened. Also catches `Assert.AreEqual(dto.Name, dto.Name)` (asserting a field against itself). |
| **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:

1. **Summary** -- Total issues found, broken down by severity (Critical / High / Medium / Low). If tests are well-written, lead with that assessment.
2. **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)
3. **Medium and Low findings** -- Summarize in a table unless the user wants full detail
4. **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:

1. **Critical** -- Fix immediately, these tests may be giving false confidence
2. **High** -- Fix soon, these cause flakiness or maintenance burden
3. **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 |