go-ratelimit/docs/development.md

Development Guide

Prerequisites

• Go 1.25 or later (the module declares go 1.25.5)
• No CGO required — modernc.org/sqlite is a pure Go port

No C toolchain, no system SQLite library, no external build tools. A plain go build ./... is sufficient.

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Build and Test

# Run all tests
go test ./...

# Run all tests with the race detector (required before every commit)
go test -race ./...

# Run a single test by name
go test -v -run TestCanSend ./...

# Run a single subtest
go test -v -run "TestCanSend/RPM_at_exact_limit_is_rejected" ./...

# Run benchmarks
go test -bench=. -benchmem ./...

# Run a specific benchmark
go test -bench=BenchmarkCanSend -benchmem ./...

# Check for vet issues
go vet ./...

# Tidy dependencies
go mod tidy

All three commands (go test -race ./..., go vet ./..., and go mod tidy) must produce no errors or warnings before a commit is pushed.

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Test Patterns

File Organisation

• ratelimit_test.go — Phase 0 (core logic) and Phase 1 (provider profiles)
• sqlite_test.go — Phase 2 (SQLite backend)

Both files are in package ratelimit (white-box tests) so they can access unexported fields and methods such as prune(), filePath, and sqlite.

Naming Convention

SQLite tests follow the _Good, _Bad, _Ugly suffix pattern:

• _Good — happy path
• _Bad — expected error conditions (invalid paths, corrupt input)
• _Ugly — panic-adjacent edge cases (corrupt DB files, truncated files)

Core logic tests use plain descriptive names without suffixes, grouped by method with table-driven subtests.

Test Helpers

newTestLimiter(t *testing.T) creates a RateLimiter with Gemini defaults and redirects the YAML file path into t.TempDir():

func newTestLimiter(t *testing.T) *RateLimiter {
    t.Helper()
    rl, err := New()
    require.NoError(t, err)
    rl.filePath = filepath.Join(t.TempDir(), "ratelimits.yaml")
    return rl
}

Use t.TempDir() for all file paths in tests. Go cleans these up automatically after each test completes.

Testify Usage

Tests use github.com/stretchr/testify exclusively:

• require.NoError(t, err) — fail immediately on setup errors
• assert.NoError(t, err) — record failure but continue
• assert.Equal(t, expected, actual, "message") — prefer over raw comparisons
• assert.True / assert.False — for boolean checks
• assert.Empty / assert.Len — for slice length checks
• assert.ErrorIs(t, err, context.DeadlineExceeded) — for sentinel errors

Do not use t.Error, t.Fatal, or t.Log directly.

Race Tests

Concurrency tests spin up goroutines and use sync.WaitGroup. They do not assert anything beyond absence of data races (the race detector does the work):

var wg sync.WaitGroup
for i := 0; i < 20; i++ {
    wg.Add(1)
    go func() {
        defer wg.Done()
        // concurrent operations
    }()
}
wg.Wait()

Run every concurrency test with -race. The CI baseline is go test -race ./... clean.

Coverage

Current coverage: 95.1%. The remaining 5% consists of three paths that cannot be covered in unit tests without modifying the production code:

1. CountTokens success path — hardcoded Google API URL requires network access
2. yaml.Marshal error path in Persist() — cannot be triggered with valid Go structs
3. os.UserHomeDir() error path in NewWithConfig() — requires unsetting $HOME

Do not lower coverage below 95% without a documented reason.

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Coding Standards

Language

UK English throughout: colour, organisation, serialise, initialise, behaviour. Do not use American spellings in identifiers, comments, or documentation.

Go Style

• All exported types, functions, and fields must have doc comments
• Error strings must be lowercase and not end with punctuation (Go convention)
• Contextual errors use fmt.Errorf("package.Function: what: %w", err) — the prefix ratelimit. is included so errors identify their origin clearly
• No init() functions
• No global mutable state outside of DefaultProfiles() (which returns a fresh map on each call)

Mutex Discipline

The RateLimiter.mu mutex is the only synchronisation primitive. Rules:

• Methods that call prune() always acquire the write lock (mu.Lock()), even if they appear read-only, because prune() mutates slices
• Persist() acquires only the read lock (mu.RLock()) because it reads a snapshot of state
• Lock acquisition always happens at the top of the public method, never inside a helper — helpers document "Caller must hold the lock"
• Never call a public method from inside another public method while holding the lock (deadlock risk)

Dependencies

Direct dependencies are intentionally minimal:

Dependency	Purpose
gopkg.in/yaml.v3	YAML serialisation for legacy backend
modernc.org/sqlite	Pure Go SQLite for persistent backend
github.com/stretchr/testify	Test assertions (test-only)

Do not add database/sql drivers beyond modernc.org/sqlite. Do not add HTTP client libraries; the existing CountTokens function uses the standard library.

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Licence

EUPL-1.2. Every new source file must carry the standard header if the project adopts per-file headers in future. Confirm with the project lead before adding files under a different licence.

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Commit Convention

Format: type(scope): description

Common types: feat, fix, test, refactor, docs, perf, chore

Common scopes: ratelimit, sqlite, persist, config

Every commit must include:

Co-Authored-By: Virgil <virgil@lethean.io>

Example:

feat(sqlite): add WAL-mode SQLite backend with migration helper

Co-Authored-By: Virgil <virgil@lethean.io>

Commits must not be pushed unless go test -race ./... and go vet ./... both pass. go mod tidy must produce no changes.