Keep each test database when the pool replaces its connection (closes #209)

SQLite deletes a shared in-memory database when its last connection
closes. A query cancelled while it runs makes the pool close its
connection, so a test could lose all its tables and rows at random.

The new package internal/dbtest has NewURL. It returns the URL of a
new in-memory database with a random name and holds one connection to
it open until the test ends. The db, handlers, ircserver, server and
service tests take their database URL from it. The test-support lint
rule keeps the package out of the server binary.

A new test cancels a query on such a database, checks with a TEMP
table that the connection was replaced, and checks that a row is
still there.

Model: opus-5-5

internal/db/db_test.go

@@ -12,6 +12,7 @@ import (
 	"go.uber.org/fx/fxtest"
 	"sneak.berlin/go/neoirc/internal/config"
 	"sneak.berlin/go/neoirc/internal/db"
+	"sneak.berlin/go/neoirc/internal/dbtest"
 	"sneak.berlin/go/neoirc/internal/globals"
 	"sneak.berlin/go/neoirc/internal/logger"
 )
@@ -155,6 +156,52 @@ func TestForeignKeysOnAfterCancelledQuery(t *testing.T) {
 	}
 }
 
+// TestNewURLKeepsDataAfterCancelledQuery cancels a query on a test
+// database while it runs, which makes the pool close its only
+// connection and open a new one. A TEMP table lasts only as long as
+// its connection, so its absence shows the connection was replaced.
+// The database must still have its tables and rows.
+func TestNewURLKeepsDataAfterCancelledQuery(t *testing.T) {
+	t.Parallel()
+
+	database, err := startDatabase(t, dbtest.NewURL(t))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = database.GetOrCreateChannel(t.Context(), "#test")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = database.GetDB().ExecContext(
+		t.Context(), "CREATE TEMP TABLE first_connection (x)",
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ctx, cancel := context.WithTimeout(t.Context(), endlessQueryTimeout)
+	defer cancel()
+
+	_, err = database.GetDB().ExecContext(ctx, endlessQuery)
+	if !errors.Is(err, context.DeadlineExceeded) {
+		t.Fatalf("endless query: err = %v", err)
+	}
+
+	tempTables := queryInt(
+		t, database, "SELECT COUNT(*) FROM sqlite_temp_schema",
+	)
+	if tempTables != 0 {
+		t.Fatal("the pool kept its first connection")
+	}
+
+	channels := queryInt(t, database, "SELECT COUNT(*) FROM channels")
+	if channels != 1 {
+		t.Errorf("channels = %d, want 1", channels)
+	}
+}
+
 // TestDBURLSettingForeignKeysFailsStartup checks that the database
 // refuses to start when DBURL sets foreign_keys itself, however it
 // is spelled.