Give each handler and service test its own database (closes #131)

Test databases in internal/handlers and internal/service were named
after the address of the running test. A later test could get the
address of a finished one, and with it a database that test's server
might still hold open. Each test database now gets a random name, as
in internal/ircserver.

A new test in each package opens two test databases at once and checks
that they do not share one; both new tests fail with the old names.

Model: opus-5-5
Co-authored-by: clawbot <sneak+clawbot@sneak.cloud>

internal/service/service_test.go

@@ -6,6 +6,7 @@ package service_test
 
 import (
 	"context"
+	"crypto/rand"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -43,9 +44,12 @@ type testEnv struct {
 func newTestEnv(t *testing.T) *testEnv {
 	t.Helper()
 
+	// A random name, so that no other test can share it, not
+	// even one that has finished but still holds its database
+	// open.
 	dbURL := fmt.Sprintf(
-		"file:svc_test_%p?mode=memory&cache=shared",
-		t,
+		"file:%s?mode=memory&cache=shared",
+		rand.Text(),
 	)
 
 	var (
@@ -137,6 +141,19 @@ func createSession(
 	return sessionID
 }
 
+// TestEachTestEnvHasItsOwnDatabase checks that a test
+// environment starts on an empty database while another one
+// is still open.
+func TestEachTestEnvHasItsOwnDatabase(t *testing.T) {
+	ctx := t.Context()
+
+	first := newTestEnv(t)
+	createSession(ctx, t, first.db, "samenick")
+
+	second := newTestEnv(t)
+	createSession(ctx, t, second.db, "samenick")
+}
+
 func TestFanOut(t *testing.T) {
 	env := newTestEnv(t)
 	ctx := t.Context()