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Test Levels

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Execution environments and test scope (L0-L4)

Test level tags define the execution environment and scope based on the Testing Taxonomy.

Test Pyramid

Test levels form a pyramid with fast, isolated tests at the bottom and slower, integrated tests at the top:

Mermaid diagram

Principle: More tests at lower levels (fast, isolated) and fewer at higher levels (slow, integrated).

Test Isolation Characteristics

Each level trades off between speed/determinism and realism:

Mermaid diagram

Level Speed Determinism Domain Coherency Use When
L0 Fastest Highest Lowest Algorithm testing
L1 Fast High Low Business logic
L2 Moderate High High Integration testing
L3 Slow Medium Highest Deployment validation
L4 Continuous Low Highest Smoke tests

@L0 - Fast Unit Tests

  • Execution: Devbox or agent
  • Scope: Source and binary
  • Dependencies: All replaced with test doubles
  • Speed: Milliseconds
  • Usage: Go tests with //go:build L0 build tag, Godog features with @L0 tag
  • Trade-off: Highest determinism, lowest domain coherency

Example:

//go:build L0
// +build L0

package mypackage_test

func TestValidateEmail(t *testing.T) {
    // Very fast unit test
}

@L1 - Unit Tests

  • Execution: Devbox or agent
  • Scope: Source and binary
  • Dependencies: All replaced with test doubles
  • Speed: Seconds
  • Usage: Go tests (default, no build tag needed), Godog features with @L1 tag
  • Trade-off: Highest determinism, lowest domain coherency

Example:

package mypackage_test

func TestUserService_CreateUser(t *testing.T) {
    // Unit test with mocked dependencies
}

@L2 - Emulated System Tests

  • Execution: Devbox or agent
  • Scope: Deployable artifacts
  • Dependencies: All replaced with test doubles
  • Speed: Seconds
  • Usage: Go tests with //go:build L2 build tag, Godog features (default if no level tag specified)
  • Trade-off: High determinism, high domain coherency

Example:

@L2 @deps:docker @ov
Feature: Container Integration Tests
  Tests requiring Docker for artifact validation

@L3 - In-Situ Vertical Tests

  • Execution: PLTE (Production-Like Test Environment)
  • Scope: Deployed system (single deployable module boundaries)
  • Dependencies: All replaced with test doubles
  • Speed: Minutes
  • Usage: Go tests with //go:build L3 build tag, Godog features with @L3 tag (automatically inferred from @iv or @pv)
  • Trade-off: Moderate determinism, high domain coherency

Example:

@L3 @iv
Feature: API Service Deployment Verification
  Validates deployment in PLTE with test doubles

@L4 - Testing in Production

  • Execution: Production
  • Scope: Deployed system (cross-service interactions)
  • Dependencies: All production, may use live test doubles
  • Speed: Continuous
  • Usage: Go tests with //go:build L4 build tag, Godog features with @L4 tag (automatically inferred from @piv or @ppv)
  • Trade-off: High determinism, highest domain coherency

Example:

@L4 @piv
Feature: Production Smoke Tests
  Validates production deployment post-release

Inference Rules

Go Tests

  • No build tag → @L1
  • //go:build L0 → @L0
  • //go:build L2 → @L2
  • //go:build L3 → @L3
  • //go:build L4 → @L4

Godog Features

  • No level tag → @L2
  • Explicit @L0, @L1, @L2, @L3, or @L4 → corresponding level
  • Features with @iv or @pv → @L3 (if no explicit level tag)
  • Features with @piv or @ppv → @L4 (if no explicit level tag)

Test Level Selection Guide

L0 - Choose When

  • Testing pure functions with no side effects
  • No I/O operations (filesystem, network, database)
  • Microsecond-level execution speed required
  • Maximum parallelization needed

L1 - Choose When

  • Unit testing with minimal mocks
  • Using temp directories or simple file I/O
  • Fast feedback loop needed (pre-commit)
  • Testing individual components in isolation

L2 - Choose When

  • Testing with emulated dependencies (test containers, mocked APIs)
  • Integration testing without real infrastructure
  • Need deterministic, repeatable results
  • CI/CD pipeline validation

L3 - Choose When

  • Deployment verification in PLTE
  • Installation validation (@iv)
  • Performance testing in production-like environment (@pv)
  • End-to-end testing with real infrastructure (test environment)

L4 - Choose When

  • Production smoke tests (@piv)
  • Continuous production monitoring (@ppv)
  • Post-deployment validation
  • Read-only production verification

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