Add tests for globals, healthcheck, and logger packages (closes #110)

These three packages had no tests. Add behavioural, external
(package foo_test) tests that can each fail on a plausible break:

- globals: setters and read-back through New, plus that New returns
  an independent snapshot. One sequential function with a disclosed
  paralleltest suppression, because it mutates shared package globals.
- healthcheck: Check returns status "ok", the exact documented JSON
  field set, an RFC3339Nano timestamp, maintenanceMode mirroring the
  config in both states, and the version and appname from globals.
- logger: New yields a usable *slog.Logger, debug is suppressed at the
  default level, and EnableDebugLogging turns it on.

No production code changed. TTY-branch output format is not asserted.

Model: opus-4-8

TODO.md

@@ -23,6 +23,8 @@ Rationale, Design, TODO, License, Author) if any are still missing.
 
 # Completed Steps
 
+- 2026-09-21: added behavioural tests for `internal/globals`,
+  `internal/healthcheck`, and `internal/logger` (closes #110).
 - 2026-09-21: `go mod tidy` dropped the redundant `golang.org/x/sync`
   `// indirect` line so `script/bootstrap` leaves a clean tree (#132)
 - 2026-08-10: comment-only corrections to `script/bootstrap`,

internal/globals/globals_test.go

@@ -0,0 +1,50 @@
+package globals_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"sneak.berlin/go/dnswatcher/internal/globals"
+)
+
+// TestGlobals exercises the package-level version and appname
+// variables through their setters and read-back via New. These are
+// shared package state, so the test mutates a global and must run
+// sequentially; it cannot use t.Parallel().
+//
+//nolint:paralleltest // mutates shared package-level globals, must run sequentially
+func TestGlobals(t *testing.T) {
+	versions := []string{"v1.2.3", "dev", "", "v1.2.3-4-gabcdef"}
+	for _, want := range versions {
+		globals.SetVersion(want)
+
+		g, err := globals.New(nil)
+		require.NoError(t, err)
+		assert.Equal(t, want, g.Version,
+			"New must surface the version set by SetVersion")
+	}
+
+	names := []string{"dnswatcher", "other", ""}
+	for _, want := range names {
+		globals.SetAppname(want)
+
+		g, err := globals.New(nil)
+		require.NoError(t, err)
+		assert.Equal(t, want, g.Appname,
+			"New must surface the appname set by SetAppname")
+	}
+
+	// New returns a snapshot: a later SetVersion must not mutate a
+	// Globals handed out earlier.
+	globals.SetVersion("first")
+
+	g, err := globals.New(nil)
+	require.NoError(t, err)
+
+	globals.SetVersion("second")
+	assert.Equal(t, "first", g.Version,
+		"a Globals returned by New must not change when the "+
+			"package variable is set again")
+}

internal/healthcheck/healthcheck_test.go

@@ -0,0 +1,134 @@
+package healthcheck_test
+
+import (
+	"context"
+	"encoding/json"
+	"testing"
+	"time"
+
+	"go.uber.org/fx"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"sneak.berlin/go/dnswatcher/internal/config"
+	"sneak.berlin/go/dnswatcher/internal/globals"
+	"sneak.berlin/go/dnswatcher/internal/healthcheck"
+	"sneak.berlin/go/dnswatcher/internal/logger"
+)
+
+// recordingLifecycle is a minimal fx.Lifecycle that records the hooks
+// appended to it, so healthcheck.New can be exercised through its real
+// constructor without standing up a whole fx application.
+type recordingLifecycle struct {
+	hooks []fx.Hook
+}
+
+func (l *recordingLifecycle) Append(hook fx.Hook) {
+	l.hooks = append(l.hooks, hook)
+}
+
+// newHealthcheck builds a Healthcheck through the real constructor and
+// runs the registered OnStart hook so StartupTime is set the same way
+// the fx lifecycle would set it.
+func newHealthcheck(
+	t *testing.T,
+	maintenance bool,
+	version string,
+) *healthcheck.Healthcheck {
+	t.Helper()
+
+	g := &globals.Globals{Appname: "dnswatcher", Version: version}
+
+	log, err := logger.New(nil, logger.Params{Globals: g})
+	require.NoError(t, err)
+
+	lifecycle := &recordingLifecycle{}
+
+	hc, err := healthcheck.New(lifecycle, healthcheck.Params{
+		Globals: g,
+		Config:  &config.Config{MaintenanceMode: maintenance},
+		Logger:  log,
+	})
+	require.NoError(t, err)
+
+	require.Len(t, lifecycle.hooks, 1,
+		"New must register exactly one lifecycle hook")
+	require.NotNil(t, lifecycle.hooks[0].OnStart)
+	require.NoError(t, lifecycle.hooks[0].OnStart(context.Background()))
+
+	return hc
+}
+
+func TestCheckStatusAndPayloadShape(t *testing.T) {
+	t.Parallel()
+
+	hc := newHealthcheck(t, false, "v9.9.9")
+	resp := hc.Check()
+
+	assert.Equal(t, "ok", resp.Status)
+
+	// The JSON shape and field names are part of the contract for the
+	// /health and /.well-known/healthcheck routes, so assert on the
+	// exact set of keys the response marshals to.
+	raw, err := json.Marshal(resp)
+	require.NoError(t, err)
+
+	var fields map[string]json.RawMessage
+	require.NoError(t, json.Unmarshal(raw, &fields))
+
+	wantKeys := []string{
+		"status",
+		"now",
+		"uptimeSeconds",
+		"uptimeHuman",
+		"version",
+		"appname",
+		"maintenanceMode",
+	}
+	assert.Len(t, fields, len(wantKeys),
+		"response must marshal to exactly the documented fields")
+
+	for _, key := range wantKeys {
+		assert.Contains(t, fields, key, "missing JSON field %q", key)
+	}
+
+	// The Now field is documented as RFC3339Nano; a change to the
+	// format constant should turn this red.
+	_, err = time.Parse(time.RFC3339Nano, resp.Now)
+	assert.NoError(t, err, "Now must be RFC3339Nano")
+}
+
+func TestCheckMaintenanceModeReflectsConfig(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name        string
+		maintenance bool
+	}{
+		{"maintenance off", false},
+		{"maintenance on", true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			hc := newHealthcheck(t, tt.maintenance, "test")
+			resp := hc.Check()
+			assert.Equal(t, tt.maintenance, resp.Maintenance,
+				"maintenanceMode must mirror Config.MaintenanceMode")
+		})
+	}
+}
+
+func TestCheckSurfacesVersionAndAppname(t *testing.T) {
+	t.Parallel()
+
+	hc := newHealthcheck(t, false, "surfaced-version-123")
+	resp := hc.Check()
+
+	assert.Equal(t, "surfaced-version-123", resp.Version,
+		"version from globals must appear in the payload")
+	assert.Equal(t, "dnswatcher", resp.Appname)
+}

internal/logger/logger_test.go

@@ -0,0 +1,66 @@
+package logger_test
+
+import (
+	"context"
+	"log/slog"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"sneak.berlin/go/dnswatcher/internal/globals"
+	"sneak.berlin/go/dnswatcher/internal/logger"
+)
+
+func newTestLogger(t *testing.T) *logger.Logger {
+	t.Helper()
+
+	g := &globals.Globals{Appname: "dnswatcher", Version: "test"}
+
+	l, err := logger.New(nil, logger.Params{Globals: g})
+	require.NoError(t, err)
+
+	return l
+}
+
+// TestNewReturnsUsableLogger checks that the constructor yields a
+// working *slog.Logger.
+func TestNewReturnsUsableLogger(t *testing.T) {
+	t.Parallel()
+
+	l := newTestLogger(t)
+	require.NotNil(t, l.Get(), "Get must return a non-nil logger")
+}
+
+// TestDefaultLevelExcludesDebug verifies the default configuration
+// logs at info: debug records are suppressed, info records pass.
+func TestDefaultLevelExcludesDebug(t *testing.T) {
+	t.Parallel()
+
+	log := newTestLogger(t).Get()
+	ctx := context.Background()
+
+	assert.False(t, log.Enabled(ctx, slog.LevelDebug),
+		"debug must be suppressed at the default level")
+	assert.True(t, log.Enabled(ctx, slog.LevelInfo),
+		"info must be enabled at the default level")
+}
+
+// TestEnableDebugLoggingChangesLevel verifies the debug and non-debug
+// configurations differ as intended: enabling debug makes debug
+// records pass where they previously did not.
+func TestEnableDebugLoggingChangesLevel(t *testing.T) {
+	t.Parallel()
+
+	l := newTestLogger(t)
+	log := l.Get()
+	ctx := context.Background()
+
+	require.False(t, log.Enabled(ctx, slog.LevelDebug),
+		"debug must start disabled")
+
+	l.EnableDebugLogging()
+
+	assert.True(t, log.Enabled(ctx, slog.LevelDebug),
+		"debug must be enabled after EnableDebugLogging")
+}