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:

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

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 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 SECTIONs 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.