test: add syntest around connection open and close

Author: GeorgeMac

clickhouse_test.go

@@ -0,0 +1,79 @@
+//go:build go1.25
+
+package clickhouse
+
+import (
+	"fmt"
+	"sync"
+	"testing"
+	"testing/synctest"
+)
+
+// TestIdleConnectionCleanupLeak demonstrates that startAutoCloseIdleConnections
+// goroutines are leaked when connections are opened and closed.
+//
+// This test uses Go's synctest package (stably available in Go 1.25+) to deterministically
+// detect the leaked goroutine without relying on timing or sleep calls.
+func TestIdleConnectionCleanupLeak(t *testing.T) {
+	synctest.Test(t, func(t *testing.T) {
+		conn, err := Open(&Options{
+			Addr: []string{"localhost:9000"},
+		})
+		if err != nil {
+			t.Fatalf("failed to open connection: %v", err)
+		}
+
+		// Close the connection - this should stop the goroutine
+		if err := conn.Close(); err != nil {
+			t.Fatalf("failed to close connection: %v", err)
+		}
+
+		// Wait for all goroutines in this synctest bubble to exit
+		// This will hang if background goroutines are left behind.
+		synctest.Wait()
+	})
+}
+
+// TestIdleConnectionCleanupLeak demonstrates that startAutoCloseIdleConnections
+// goroutines are leaked when connections are opened and closed.
+//
+// This test uses Go's synctest package (stably available in Go 1.25+) to deterministically
+// detect the leaked goroutine without relying on timing or sleep calls.
+func TestIdleConnectionCleanupLeakConcurrent(t *testing.T) {
+	synctest.Test(t, func(t *testing.T) {
+		errs := make(chan error)
+
+		var wg sync.WaitGroup
+		for range 100 {
+			wg.Add(1)
+			go func() {
+				defer wg.Done()
+				conn, err := Open(&Options{
+					Addr: []string{"localhost:9000"},
+				})
+				if err != nil {
+					errs <- fmt.Errorf("failed to open connection: %w", err)
+				}
+
+				// Close the connection - this should stop the goroutine
+				if err := conn.Close(); err != nil {
+					errs <- fmt.Errorf("failed to close connection: %w", err)
+				}
+			}()
+		}
+
+		go func() {
+			wg.Wait()
+			close(errs)
+		}()
+
+		for err := range errs {
+			// any error attempting to open or close should be fatal
+			t.Fatal(err)
+		}
+
+		// Wait for all goroutines in this synctest bubble to exit
+		// This will hang if background goroutines are left behind.
+		synctest.Wait()
+	})
+}