tests: move the test-only constructors into export_test.go (closes #111)

state.NewForTest, state.NewForTestWithDataDir and watcher.NewForTest
were in ordinary source files, so they were built into the binary.
NewForTestWithDataDir and watcher.NewForTest now live in their
package's export_test.go. Tests in other packages cannot see those
files, so the watcher and middleware tests build their State with
state.New and a temporary data directory; the watcher tests no longer
try to save to /state.json. state.NewForTest, whose State saved to /,
is deleted: the state tests that used it pass t.TempDir() to
NewForTestWithDataDir, and the test of the helper itself is gone.

Model: opus-5-5

internal/watcher/export_test.go

@@ -2,10 +2,35 @@ package watcher
 
 import (
 	"context"
+	"log/slog"
+	"time"
 
+	"sneak.berlin/go/dnswatcher/internal/config"
 	"sneak.berlin/go/dnswatcher/internal/state"
 )
 
+// NewForTest creates a Watcher without fx for unit testing.
+func NewForTest(
+	cfg *config.Config,
+	st *state.State,
+	res DNSResolver,
+	pc PortChecker,
+	tc TLSChecker,
+	n Notifier,
+) *Watcher {
+	return &Watcher{
+		log:            slog.Default(),
+		config:         cfg,
+		state:          st,
+		resolver:       res,
+		portCheck:      pc,
+		tlsCheck:       tc,
+		notify:         n,
+		firstRun:       true,
+		expiryNotified: make(map[string]time.Time),
+	}
+}
+
 // NewlyDisagreeingPairs exports newlyDisagreeingPairs for testing.
 func NewlyDisagreeingPairs(
 	prev *state.HostnameState,