test-smell-detection

# Test Smell Detection Deep formal audit of test code in any supported language using an academic test smell taxonomy. Detects symptoms of bad design or implementation decisions that make tests harder to understand, more fragile, less effective at catching bugs, or more expensive to maintain. Produces a severity-ranked report with specific locations and actionable fixes. > **Language-specific guidance**: Call the `test-analysis-extensions` skill to discover available extension files, then read the file matching the target codebase. The extension file documents test markers, sleep / time / random APIs, skip annotations, setup/teardown, mystery-guest indicators (file/database/network/env), integration markers, and language-specific calibration notes that drive the smell detectors below. ## Why Test Smells Matter Test smells erode confidence in a test suite and inflate maintenance costs: | Problem | Consequence | |---------|-------------| | Tests with conditional logic | Some paths never execute — hidden testing gaps | | Tests that depend on external resources | Flaky failures, slow execution, environment coupling | | Tests that sleep to wait for results | Non-deterministic timing, slow suites, false failures | | Tests without assertions | False confidence — coverage looks good but nothing is verified | | Tests that call many production methods | Hard to diagnose failures, unclear what's being tested | | Tests with magic numbers | Unreadable intent, unclear boundary conditions | | Tests relying on ToString for comparison | Brittle to formatting changes, obscure failure messages | | Tests with exception handling logic | Swallowed failures, tests that pass when they shouldn't | ## When to Use - User asks for a comprehensive or formal test smell audit - User asks "are my tests well-written?" and wants a thorough analysis - User wants a test quality health check with academic rigor - User asks for a review of test design or structure using standard smell categories - User suspects tests are fragile, flaky, or giving false confidence and wants a deep investigation ## When Not to Use - User wants a quick pragmatic test review (use `test-anti-patterns` — faster, covers the most common issues) - User wants to evaluate assertion diversity specifically (use `assertion-quality`) - User wants to find duplicated boilerplate across tests (use `exp-test-maintainability`) - User wants to write new tests from scratch (help them directly) - User wants to fix a specific failing test (diagnose and fix directly) ## 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 whether patterns are justified | ## Workflow ### Step 1: Detect language and load extension Identify the target codebase's language and test framework. Call the `test-analysis-extensions` skill and read the matching extension file (e.g., `extensions/dotnet.md`, `extensions/python.md`, `extensions/typescript.md`, `extensions/go.md`). The extension file lists the framework-specific test markers, sleep / wait APIs, skip / ignore attributes, mystery-guest indicators, and integration-test markers that the smell detectors below need. ### Step 2: Gather the test code Read all test files the user provides. If the user points to a directory or project, scan for all test files using the markers in the loaded language extension file. For a thorough audit, also consult the [extended smell catalog](references/test-smell-catalog.md) which covers 9 additional smell types beyond the core 10 below. ### Step 3: Scan for test smells For each test method and class, check for the following smell categories. Examples reference .NET attributes but the patterns apply across all supported languages — use the loaded language extension file to map each pattern to the framework you are auditing. #### Smell 1: Conditional Test Logic Test methods containing `if`, `else`, `switch`, ternary (`? :`), `for`, `foreach`, `while`, or pattern-match arms that change assertion behavior. Control flow in tests means some paths may never execute, hiding gaps. **Severity:** High **Detection:** Any control-flow statement inside a test method body that affects which assertions run. **Exceptions (per-language idioms, do NOT flag):** - **Foreach-assert** used solely to assert every item in a known collection (the assertion *is* the loop body). - **Go / Rust table-driven tests**: `for _, tt := range tests { t.Run(tt.name, func(t *testing.T) { ... }) }` (Go) or `#[rstest]` parametrized loops are idiomatic. - **`it.each(...)` / `test.each(...)` / `@pytest.mark.parametrize` / `[Theory] + [InlineData]` / `@ParameterizedTest`** parametrization driven by data tables. - **Pester `-ForEach` / `-TestCases`** and **RSpec `where` blocks**. - **Catch2 `SECTION`s and `GENERATE(...)`**, **doctest `SUBCASE`**, **GoogleTest `INSTANTIATE_TEST_SUITE_P`**. #### Smell 2: Mystery Guest Tests that depend on external resources — files on disk, databases, network endpoints, environment variables — without making the dependency explicit or using test doubles. **Severity:** High **Detection:** Test methods that read files, open database connections, make HTTP requests (without a test handler), read environment variables, or use hard-coded file paths. Per language: `File.ReadAllText` / `Directory.GetFiles` / `HttpClient` / `Environment.GetEnvironmentVariable` (.NET); `open()` / `pathlib.Path.read_text()` / `requests.get()` / `os.environ[...]` (Python); `fs.readFileSync` / `fetch(...)` / `process.env.X` (JS/TS); `Files.readAllBytes` / `Files.newInputStream` / `HttpClient.send` / `System.getenv` (Java); `os.ReadFile` / `http.Get` / `os.Getenv` (Go); `File.read` / `Net::HTTP.get` / `ENV[...]` (Ruby); `std::fs::read_to_string` / `reqwest::get` / `std::env::var` (Rust); `String(contentsOfFile:)` / `URLSession.shared.data` / `ProcessInfo.processInfo.environment` (Swift); `File(...).readText()` / `URL(...).openConnection()` / `System.getenv` (Kotlin); `Get-Content` / `Invoke-WebRequest` / `$env:X` (Pester); `std::ifstream` / `curl_easy_perform` / `std::getenv` (C++). **Exception:** In-memory fakes, test-specific handlers, or hermetic test data factories are fine. #### Smell 3: Sleepy Test Tests that call sleep or delay functions to wait for a condition. These introduce non-deterministic timing and slow down the suite. **Severity:** High **Detection:** Calls to sleep/delay functions inside test methods: `Thread.Sleep` / `Task.Delay` (.NET); `time.sleep` / `asyncio.sleep` (Python); `setTimeout` / `await new Promise(r => setTimeout(...))` / `jest.advanceTimersByTime` not paired with a wait (JS/TS); `Thread.sleep` / `TimeUnit.SECONDS.sleep` (Java); `time.Sleep` (Go); `sleep` / `Kernel#sleep` (Ruby); `std::thread::sleep` / `tokio::time::sleep` (Rust); `Thread.sleep` / `delay` (Kotlin coroutines); `sleep(_:)` / `Task.sleep` (Swift); `Start-Sleep` (Pester); `std::this_thread::sleep_for` (C++). See the matching language extension file for the full list. #### Smell 4: Assertion-Free Test (Unknown Test) Tests that execute code but never assert anything. Test frameworks report these as passing even if the code is completely broken, as long as no exception is thrown. **Severity:** High **Detection:** A test method with no assertion calls and no expected-exception annotation. Framework-specific: missing `Assert.*` (.NET); no `assert` / `pytest.raises` (Python); no `expect(...)` or `assert.*` (JS/TS); no `assert*` / `assertThat` (Java); no `t.Error*` / `t.Fatal*` / `assert.*` testify (Go); no `expect`/`.to`/`.eq` (RSpec) or `assert*`/`refute*` (Minitest); no `assert*!` / `assert_eq!` / `panic!` (Rust); no `XCTAssert*` / `#expect` (Swift); no `assert*` / `should*` / Kotest matchers (Kotlin); no `Should -*` (Pester); no `EXPECT_*` / `ASSERT_*` / `REQUIRE` / `CHECK` (C++). **Calibration:** - A method named `*_DoesNotThrow` / `*_no_exception` / `should not throw` is implicitly asserting no exception — still flag it but note it may be intentional. - **Mock-call verifications count as assertions**: `mock.Verify(...)` (Moq), `Mock.AssertWasCalled` (NSubstitute), `mock.assert_called_with(...)` (Python), `expect(mock).toHaveBeenCalledWith(...)` (Jest), `verify(mock).method(...)` (Mockito), `Should -Invoke` (Pester) — do NOT flag tests using these as assertion-free. - **Bare assertion forms count**: `assert x == y` (pytest), `if got != want { t.Errorf(...) }` (Go), `assert!(cond)` (Rust) are canonical. - **Snapshot assertions count**: `.toMatchSnapshot()` (Jest), `syrupy` (pytest), `SnapshotTesting` (Swift), `approval-tests` are real assertions. - **Missing await on async assertions is its own critical smell**: `expect(promise).resolves.toBe(x)` without `await`/`return` (Jest), un-awaited `Assert.ThrowsAsync` (xUnit), un-awaited coroutines in `pytest-asyncio`, Kotest tests without `runTest`, Swift Testing async cases without `await`. These tests have assertion calls but silently pass — flag with a dedicated note. #### Smell 5: Eager Test A test method that calls many different production methods, making it unclear what behavior is being tested. When it fails, diagnosis is difficult because the failure could stem from any of the calls. **Severity:** Medium **Detection:** A test method that calls 4+ distinct methods on the production object (excluding setup/construction). Count unique method names, not call count. **Calibration:** Integration / end-to-end / workflow tests may legitimately call multiple methods. Check for integration markers in the loaded language extension file (e.g., `[Trait("Category", "Integration")]`, `@Tag("integration")`, `pytest.mark.integration`, `*_integration_test.go`, `Describe ... -Tag 'Integration'`) and downgrade. #### Smell 6: Magic Number Test Assertions that contain unexplained numeric literals. The intent of `Assert.AreEqual(42, result)` / `assert result == 42` / `expect(result).toBe(42)` is unclear without context — what does 42 represent? **Severity:** Medium **Detection:** Numeric literals (other than 0, 1, -1, and the literal used in the test name) appearing as `expected` parameters in assertion methods or comparison operands. **Calibration:** Small integers in context (like count checks `Assert.AreEqual(3, list.Count)` / `assert len(items) == 3` / `expect(arr.length).toBe(3)` where 3 items were just added) are acceptable — only flag when the number's meaning is genuinely unclear. #### Smell 7: Sensitive Equality Tests that use string conversion for comparison or assertion. If the underlying string representation changes, the test breaks even though the actual behavior is correct. **Severity:** Medium **Detection:** `Assert.AreEqual(expected, obj.ToString())` (.NET); `assert str(obj) == "..."` or `assert repr(obj) == "..."` (Python); `expect(obj.toString()).toBe("...")` or `expect(`${obj}`).toBe(...)` (JS/TS); `assertEquals(expected, obj.toString())` (Java); `assert.Equal(t, "...", fmt.Sprint(obj))` or `obj.String()` chains (Go); `expect(obj.to_s).to eq("...")` (RSpec); `assert_eq!(format!("{}", obj), "...")` or `assert_eq!(format!("{:?}", obj), "...")` (Rust); `XCTAssertEqual(obj.description, "...")` or string-interpolation assertion (Swift); `assertEquals("...", obj.toString())` (Kotlin); `Should -Be "..."` against a `[string]$obj` (Pester); `EXPECT_EQ("...", std::to_string(obj))` (C++). #### Smell 8: Exception Handling in Tests Tests that contain `try`/`catch`/`except`/`rescue` blocks or `throw`/`raise`/`panic`/`return err` statements used to manage exception flow instead of asserting on it. This typically means the test is manually managing errors rather than using the framework's built-in exception assertion facilities. **Severity:** Medium **Detection:** `try`/`catch` (.NET, Java, JS/TS, Kotlin, Swift, C++); `try`/`except` (Python); `begin`/`rescue` (Ruby); `defer recover()` (Go); manual `if err != nil { t.Fatal(err) }` in Go is canonical and NOT a smell. **Exception:** `catch`/`except`/`rescue` blocks that capture an exception for further assertion on its properties are a lesser concern — note but don't flag as high severity. #### Smell 9: General Fixture (Over-broad Setup) The test setup method, constructor, or fixture initializes fields that are not used by every test method. This means each test pays the cost of setting up objects it doesn't need. **Severity:** Low **Detection:** Fields/properties initialized in `[TestInitialize]` / `setUp` / `@BeforeEach` / `beforeEach` / `before(:each)` / `BeforeEach` (Pester) / `setUpWithError` (XCTest) / pytest `fixture(autouse=True)` / xUnit constructor / Kotest `beforeTest` that are referenced by fewer than half the test methods in the class/module/file. #### Smell 10: Ignored / Disabled / Skipped Test Tests marked as skipped or disabled. These add overhead and clutter, and the underlying issue they were disabled for may never be addressed. **Severity:** Low