feat(shared-skills): add user skill sources

2026-05-26 20:28:24 +09:00
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+# Testing
+
+TDD shape, table-driven tests, `require` vs `assert`, snapshot tests, property-based tests, integration tests with testcontainers, goroutine-leak detection. The discipline in `programming/SKILL.md` (Given/When/Then, less mock the better, efficient AND accurate) — this document gives the Go-specific recipes.
+
+---
+
+## Tools
+
+| Need | Use |
+|---|---|
+| Assertions | `stretchr/testify/require` (and `assert` only inside table loops) |
+| Mocks | `go.uber.org/mock` (gomock successor) |
+| Goroutine leaks | `go.uber.org/goleak` |
+| Snapshots / golden | `hexops/autogold/v2` |
+| Property-based | `pgregory.net/rapid` |
+| HTTP mocks (outbound) | `h2non/gock` |
+| HTTP test server (inbound) | stdlib `net/http/httptest` |
+| Integration containers | `testcontainers/testcontainers-go` |
+| TUI | `charm.land/bubbletea/v2/teatest` |
+| Bench tooling | stdlib `testing.B` + `perf.dev/benchstat` |
+
+---
+
+## Test naming — Given / When / Then in the name
+
+```go
+// ──── PATTERN ────
+// Test_<Subject>_<Outcome>_when_<Condition>
+//   OR
+// Test_<Subject>_<Action>_<ExpectedOutcome>
+
+func Test_Email_NewEmail_lowercases_input(t *testing.T)
+func Test_Email_NewEmail_rejects_input_without_at_sign(t *testing.T)
+func Test_UserService_Create_persists_user_when_inputs_valid(t *testing.T)
+func Test_UserService_Create_returns_validation_error_when_email_invalid(t *testing.T)
+```
+
+A test name should answer "what behavior is this asserting?" without reading the body. Names that need a comment to explain them are misnamed.
+
+---
+
+## Single test — explicit Given/When/Then
+
+```go
+func Test_Email_NewEmail_rejects_input_without_at_sign(t *testing.T) {
+    // Given
+    raw := "not-an-email"
+
+    // When
+    _, err := domain.NewEmail(raw)
+
+    // Then
+    require.Error(t, err)
+    require.ErrorIs(t, err, domain.ErrInvalidEmail)
+}
+```
+
+`require.*` fails the test immediately on miss. Use `require` for preconditions and primary assertions. Use `assert.*` only inside table-driven loops where you want all cases to report.
+
+---
+
+## Table-driven tests
+
+```go
+func Test_Email_NewEmail(t *testing.T) {
+    tests := []struct {
+        name    string
+        input   string
+        want    string
+        wantErr error
+    }{
+        {"lowercases", "ALICE@example.com", "alice@example.com", nil},
+        {"trims whitespace", "  bob@example.com  ", "bob@example.com", nil},
+        {"rejects missing @", "no-at-sign", "", domain.ErrInvalidEmail},
+        {"rejects empty", "", "", domain.ErrInvalidEmail},
+        {"rejects too long", strings.Repeat("a", 256) + "@e.com", "", domain.ErrInvalidEmail},
+    }
+    for _, tt := range tests {
+        t.Run(tt.name, func(t *testing.T) {
+            // When
+            got, err := domain.NewEmail(tt.input)
+
+            // Then
+            if tt.wantErr != nil {
+                require.ErrorIs(t, err, tt.wantErr)
+                return
+            }
+            require.NoError(t, err)
+            assert.Equal(t, tt.want, got.String())
+        })
+    }
+}
+```
+
+Rules:
+
+- One **scenario** per row, not one **assertion** per row.
+- Subtest names are sentences in lowercase; `t.Run(tt.name, ...)` makes them filterable: `go test -run Test_Email_NewEmail/rejects_missing_@`.
+- The loop body itself is Given/When/Then in shape.
+- For Go 1.22+, the loop var capture works correctly without the `tt := tt` shadow line — the `copyloopvar` linter enforces the new style.
+
+---
+
+## Less mocks — the priority order
+
+In Go specifically:
+
+1. **Real implementation.** Domain types, pure functions, value objects — instantiate them. They are fast.
+2. **In-memory fake** that satisfies the interface. Has its own test suite proving behavioral parity with the real impl.
+3. **`httptest.Server`** for HTTP collaborators (real wire, no internet).
+4. **`testcontainers`** for stateful collaborators (Postgres, Redis, S3-compatible, Kafka).
+5. **gomock** ONLY for: clocks, randomness, third-party SaaS with no sandbox.
+
+### Example: an in-memory fake
+
+```go
+// Real interface
+type UserRepo interface {
+    Save(ctx context.Context, u domain.User) error
+    Get(ctx context.Context, id domain.UserID) (domain.User, error)
+}
+
+// In-memory fake — production-quality, tested separately
+type FakeUserRepo struct {
+    mu    sync.RWMutex
+    users map[domain.UserID]domain.User
+}
+
+func NewFakeUserRepo() *FakeUserRepo {
+    return &FakeUserRepo{users: map[domain.UserID]domain.User{}}
+}
+
+func (r *FakeUserRepo) Save(ctx context.Context, u domain.User) error {
+    r.mu.Lock(); defer r.mu.Unlock()
+    r.users[u.ID] = u
+    return nil
+}
+
+func (r *FakeUserRepo) Get(ctx context.Context, id domain.UserID) (domain.User, error) {
+    r.mu.RLock(); defer r.mu.RUnlock()
+    u, ok := r.users[id]
+    if !ok { return domain.User{}, domain.ErrUserNotFound }
+    return u, nil
+}
+```
+
+The fake has the same observable behavior as the real one. Tests against `FakeUserRepo` survive when the production repo's internals change. Tests against a gomock stub of `UserRepo` break.
+
+**A test passing against a fake AND a test passing against the real impl is the gold standard.** Run the same test suite twice — once with the fake, once with testcontainers. The fakes earn their keep when the suites diverge.
+
+### Example: gomock for the unmockable
+
+```go
+//go:generate mockgen -source=clock.go -destination=mocks/clock_mock.go -package=mocks
+
+type Clock interface {
+    Now() time.Time
+}
+
+// In a test:
+ctrl := gomock.NewController(t)
+clock := mocks.NewMockClock(ctrl)
+clock.EXPECT().Now().Return(fixedTime).AnyTimes()
+```
+
+Mock the narrowest seam. Never mock `UserRepo` if a fake suffices.
+
+---
+
+## E2E scenario tests
+
+```go
+//go:build e2e
+
+func Test_E2E_user_can_signup_then_login(t *testing.T) {
+    // Given — full server in a goroutine
+    ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+    defer cancel()
+
+    pool := newTestDB(t)              // testcontainers Postgres
+    server := startServer(t, pool)    // real gin engine on a random port
+    defer server.Close()
+
+    client := server.Client()
+
+    // When — sign up
+    resp, err := client.Post(server.URL+"/api/v1/users",
+        "application/json",
+        strings.NewReader(`{"email":"a@b.com","username":"alice","password":"PassWord!23"}`),
+    )
+    require.NoError(t, err)
+    require.Equal(t, 201, resp.StatusCode)
+
+    // When — log in
+    resp, err = client.Post(server.URL+"/api/v1/auth/login",
+        "application/json",
+        strings.NewReader(`{"email":"a@b.com","password":"PassWord!23"}`),
+    )
+    require.NoError(t, err)
+    require.Equal(t, 200, resp.StatusCode)
+
+    var body struct{ Token string `json:"token"` }
+    require.NoError(t, json.NewDecoder(resp.Body).Decode(&body))
+    require.NotEmpty(t, body.Token)
+
+    // Then — token works on protected endpoint
+    req, _ := http.NewRequestWithContext(ctx, "GET", server.URL+"/api/v1/me", nil)
+    req.Header.Set("Authorization", "Bearer "+body.Token)
+    resp, err = client.Do(req)
+    require.NoError(t, err)
+    require.Equal(t, 200, resp.StatusCode)
+}
+```
+
+Patterns:
+
+- `//go:build e2e` build tag separates slow E2E from fast unit tests. Run with `go test -tags=e2e ./...`.
+- One narrative per test: "user can sign up then log in". One `Test_E2E_*` per user-visible outcome.
+- Real DB via testcontainers, real gin engine, real HTTP. **No mocks.** The point is to catch integration bugs.
+- Bounded context — every E2E gets a `context.WithTimeout` so failures don't hang CI.
+
+---
+
+## Goroutine leak detection
+
+```go
+package mypkg
+
+import (
+    "testing"
+    "go.uber.org/goleak"
+)
+
+func TestMain(m *testing.M) {
+    goleak.VerifyTestMain(m,
+        goleak.IgnoreTopFunction("github.com/prometheus/client_golang/prometheus.(*Registry)..."),
+    )
+}
+```
+
+One line at the top of every package that spawns goroutines. Catches the bug class the race detector cannot.
+
+---
+
+## Snapshot / golden tests — `autogold`
+
+```go
+import "github.com/hexops/autogold/v2"
+
+func Test_RenderHelp_matches_snapshot(t *testing.T) {
+    // Given
+    cmd := newRootCmd()
+
+    // When
+    out := captureOutput(t, func() { _ = cmd.Help() })
+
+    // Then
+    autogold.ExpectFile(t, out)
+}
+```
+
+First run: `go test -update ./...` writes `testdata/Test_RenderHelp.golden`. Future runs compare; failures show a diff. Re-approve intentional changes with `-update`.
+
+**Use snapshots for STRUCTURE, not BEHAVIOR.** Good targets:
+
+- CLI `--help` output
+- JSON response shape
+- Generated SQL queries
+- Rendered prompts (assert the structure, not exact wording — see SKILL.md prompt-test rule)
+
+Bad targets: a function's return value where you should `require.Equal` on the actual structure.
+
+---
+
+## Property-based tests — `rapid`
+
+```go
+import "pgregory.net/rapid"
+
+func Test_Email_NewEmail_then_String_roundtrips(t *testing.T) {
+    rapid.Check(t, func(t *rapid.T) {
+        // Given — generate valid emails
+        local  := rapid.StringMatching(`[a-z]{3,10}`).Draw(t, "local")
+        domain := rapid.StringMatching(`[a-z]{3,10}\.com`).Draw(t, "domain")
+        raw    := local + "@" + domain
+
+        // When
+        e, err := domain.NewEmail(raw)
+        require.NoError(t, err)
+
+        // Then — round-trip property
+        e2, err := domain.NewEmail(e.String())
+        require.NoError(t, err)
+        require.Equal(t, e, e2)
+    })
+}
+```
+
+`rapid` shrinks failing cases to minimal counterexamples. Use for:
+
+- Round-trips (parse → serialize → parse).
+- Algebraic properties (sort produces ordered, dedup is idempotent, JSON marshal/unmarshal is involutive).
+- Invariants under random input (validator never panics, serializer never produces invalid UTF-8).
+
+---
+
+## HTTP testing — `httptest`
+
+### Server side
+
+```go
+func Test_GetUser_returns_user_for_existing_id(t *testing.T) {
+    // Given
+    svc := newSvcWithFake(t)
+    r := gin.New()
+    h := &Handler{Users: svc}
+    h.Mount(r)
+
+    req := httptest.NewRequest("GET", "/api/v1/users/u-1", nil)
+    rec := httptest.NewRecorder()
+
+    // When
+    r.ServeHTTP(rec, req)
+
+    // Then
+    require.Equal(t, 200, rec.Code)
+    var body domain.User
+    require.NoError(t, json.Unmarshal(rec.Body.Bytes(), &body))
+    require.Equal(t, "u-1", string(body.ID))
+}
+```
+
+### Client side — `httptest.NewServer`
+
+```go
+func Test_Client_retries_on_500(t *testing.T) {
+    // Given — fake upstream
+    var calls int
+    srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+        calls++
+        if calls < 3 {
+            w.WriteHeader(500)
+            return
+        }
+        w.WriteHeader(200)
+        _, _ = w.Write([]byte(`{"ok":true}`))
+    }))
+    defer srv.Close()
+
+    client := myclient.New(srv.URL)
+
+    // When
+    err := client.DoSomething(context.Background())
+
+    // Then
+    require.NoError(t, err)
+    require.Equal(t, 3, calls)
+}
+```
+
+`httptest.NewServer` spins a real HTTP server on a random port. The fake handler implements the upstream contract. Test the client against the contract, not the implementation.
+
+---
+
+## Determinism — the cardinal rules
+
+- **No `time.Sleep` in tests.** If you need delay, you need a Clock injection.
+- **`go test -shuffle=on`** in every CI run.
+- **`go test -count=1`** to defeat the cache.
+- **Subscribe to the event, do not poll for it.** Channels, callbacks, `t.Cleanup` over polling.
+- **`t.Parallel()`** for tests that share no state. Speeds up large suites by 4-8x.
+
+A test that fails 1-in-10 runs is a bug, not flake. The race detector + `-shuffle=on` + ordering hygiene catches >95% of "flake".
+
+---
+
+## Benchmarks — `testing.B` + `benchstat`
+
+```go
+func Benchmark_NewEmail(b *testing.B) {
+    for b.Loop() {  // Go 1.24+ idiom, replaces `for i := 0; i < b.N; i++`
+        _, _ = domain.NewEmail("alice@example.com")
+    }
+}
+```
+
+Run:
+
+```bash
+go test -bench=. -count=10 -benchmem ./... | tee bench.txt
+benchstat bench.txt   # statistical comparison
+```
+
+Always `-count=10` for stable means. `-benchmem` reports allocations. A 5%-slower benchmark in one run is noise; 10 runs + benchstat tells you what is real.
+
+To compare before/after a change:
+
+```bash
+git stash
+go test -bench=. -count=10 ./... > before.txt
+git stash pop
+go test -bench=. -count=10 ./... > after.txt
+benchstat before.txt after.txt
+```
+
+---
+
+## Coverage — the right target
+
+Run:
+
+```bash
+go test -race -shuffle=on -coverprofile=cover.out ./...
+go tool cover -html=cover.out -o cover.html
+```
+
+**Aim for 80%+ on `internal/domain` and `internal/service`.** Boundary code (handlers, store mappers) is exercised by integration tests, where line coverage understates what is actually verified. Do not chase 100% — the last 5% is usually error paths that need fault-injection to hit.
+
+The `golangci-lint` config does not enforce a minimum — coverage as a CI gate becomes a goal-displacement metric. Treat it as feedback, not requirement.
+
+---
+
+## TUI testing — `teatest`
+
+```go
+import teatest "charm.land/bubbletea/v2/teatest"
+
+func Test_Counter_increments_on_space(t *testing.T) {
+    // Given
+    tm := teatest.NewTestModel(t, initial(), teatest.WithInitialTermSize(80, 24))
+
+    // When
+    tm.Send(tea.KeyPressMsg{Code: ' '})
+
+    // Then
+    final := tm.FinalModel(t).(model)
+    require.Equal(t, 1, final.count)
+}
+```
+
+For full-view regression, snapshot the rendered output via `autogold`.
+
+---
+
+## Antipatterns the skill rejects
+
+| Bad | Why | Good |
+|---|---|---|
+| `if got != want { t.Errorf("expected %v got %v", want, got) }` | Reinvents `require.Equal` | Use testify |
+| `time.Sleep(100 * time.Millisecond)` after triggering async work | Flake | Subscribe to completion signal, bounded await |
+| `t.Skip(...)` to silence a known failure | Buries the bug | Fix or open an issue; never silently skip |
+| One mega-test asserting 12 things | First failure hides next 11 | Split by `Then` |
+| Snapshot-everything | Locks formatting, not behavior | Snapshots for structure, asserts for values |
+| Mock every collaborator | Test asserts implementation, not behavior | Real or fake, never mock everything |
+| Test calls private function via `_test.go` in same package only | Couples test to implementation | Test through the public surface |
+
+---
+
+## Sources
+
+- testify: https://github.com/stretchr/testify
+- goleak: https://github.com/uber-go/goleak
+- autogold: https://github.com/hexops/autogold
+- rapid: https://pkg.go.dev/pgregory.net/rapid
+- testcontainers-go: https://golang.testcontainers.org
+- benchstat: https://pkg.go.dev/golang.org/x/perf/cmd/benchstat
+- "Go test naming conventions" (Dave Cheney): https://dave.cheney.net/practical-go/presentations/qcon-china.html