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

internal/handlers/api_test.go

@@ -7,6 +7,7 @@ package handlers_test
 import (
 	"bytes"
 	"context"
+	"crypto/rand"
 	"database/sql"
 	"encoding/json"
 	"errors"
@@ -152,9 +153,12 @@ func newTestServerWith(
 ) *testServer {
 	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:test_%p?mode=memory&cache=shared",
-		t,
+		"file:%s?mode=memory&cache=shared",
+		rand.Text(),
 	)
 	copyTemplateDB(t, dbURL)
 
@@ -667,6 +671,29 @@ func TestCreateSessionDuplicate(t *testing.T) {
 	}
 }
 
+// TestEachTestServerHasItsOwnDatabase checks that starting a
+// second test server leaves the first one's database alone and
+// starts on an empty one of its own.
+func TestEachTestServerHasItsOwnDatabase(t *testing.T) {
+	first := newTestServer(t)
+	first.createSession("samenick")
+
+	second := newTestServer(t)
+
+	resp := postSession(t, first, "samenick")
+
+	defer func() { _ = resp.Body.Close() }()
+
+	if resp.StatusCode != http.StatusConflict {
+		t.Fatalf(
+			"first server: expected 409, got %d",
+			resp.StatusCode,
+		)
+	}
+
+	second.createSession("samenick")
+}
+
 func TestCreateSessionEmpty(t *testing.T) {
 	tserver := newTestServer(t)