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Testing And Coverage

Lanterna uses layered verification because a profiler has both pure analysis code and real process-instrumentation paths.

Test Layers

  • Unit and model tests cover report schemas, detector thresholds, attribution, source maps, async analysis, memory analysis, and renderer contracts.
  • Live CLI tests exercise real spawn/attach flows against small Node programs.
  • Example E2E tests run documented workloads through the locally built CLI, including positive findings, fixed negative variants, attach mode, and agent output.
  • test:e2e:smoke runs a representative CPU, memory, and async subset plus attach and agent checks for PR/release gates.
  • The scheduled/manual E2E workflow runs the full example suite.

Coverage Gate

npm run test:coverage enforces global thresholds:

Metric Threshold
Statements 70%
Branches 60%
Functions 70%
Lines 70%

These thresholds are intentionally modest. They catch broad regressions without pretending that coverage tooling fully observes code injected into target processes.

Known Low-Coverage Hotspots

The following areas are critical to capture reliability and need explicit attention when they change:

Area Why coverage is low Required evidence when changed
core/src/inspector/client.ts Real CDP behavior is also exercised through live tests. Covered by fake-CDP unit tests in test/inspector-client.test.ts (send proxy, send-after-close, evaluate, event subscribe/unsubscribe + error swallowing, onClose fire-once, idempotent close, graceful-close timeout → terminate). Extend those when changing the client.
core/src/capture/core/{cpu,heap}.ts Thin CDP measure wrappers. Covered by test/capture-measures.test.ts (command order + interval params + returned profile).
core/src/runtime-signals/hooks/** Hook source is serialized and evaluated inside the target process; V8 coverage for the host test runner does not see most executed target code. Add live tests asserting emitted integrity, cleanup, and degradation fields, or document a deliberate exclusion.
core/src/kinds/*/probe.ts Probe lifecycles depend on CDP domains and target timing. Add lifecycle tests with a fake CDP client for failure paths, plus live checks for successful captures.
core/src/capture/** (shutdown) Shutdown, timeout, signal, and process-management paths are hard to hit deterministically. Add targeted timeout/signal tests or E2E coverage with retained failure artifacts.

Rules For Future Changes

  • Do not exclude a low-coverage file just to raise the percentage.
  • If code is excluded because it is injected into a target, add a note in this document naming the live/E2E test that covers it.
  • Any new profile kind should ship at least one unit test for analysis, one schema test for its report section, and one live or E2E capture path.
  • Any new built-in detector must be added to examples/manifest.mjs; the normal test suite enforces this through examples.coverage.test.ts.

Commands

npm test
npm run test:coverage
npm run test:e2e:smoke
npm run test:e2e