diff --git a/date_test.go b/date_test.go
index e775dfc..bad7c0b 100644
--- a/date_test.go
+++ b/date_test.go
@@ -3,6 +3,7 @@ package zenity_test
 import (
 	"context"
 	"errors"
+	"fmt"
 	"os"
 	"testing"
 	"time"
@@ -17,7 +18,7 @@ func ExampleCalendar() {
 	// Output:
 }
 
-func TestCalendarTimeout(t *testing.T) {
+func TestCalendar_timeout(t *testing.T) {
 	defer goleak.VerifyNone(t)
 	ctx, cancel := context.WithTimeout(context.Background(), time.Second/5)
 	defer cancel()
@@ -31,7 +32,7 @@ func TestCalendarTimeout(t *testing.T) {
 	}
 }
 
-func TestCalendarCancel(t *testing.T) {
+func TestCalendar_cancel(t *testing.T) {
 	defer goleak.VerifyNone(t)
 	ctx, cancel := context.WithCancel(context.Background())
 	cancel()
@@ -44,3 +45,36 @@ func TestCalendarCancel(t *testing.T) {
 		t.Error("was not canceled:", err)
 	}
 }
+
+func TestCalendar_script(t *testing.T) {
+	tests := []struct {
+		name string
+		call string
+		opts []zenity.Option
+		want time.Time
+		err  error
+	}{
+		{name: "Cancel", call: "cancel", err: zenity.ErrCanceled},
+		{name: "Black", call: "choose today", want: time.Now()},
+		{name: "Rebecca", call: "press OK", want: time.Date(2000, 1, 1, 0, 0, 0, 0, time.Local),
+			opts: []zenity.Option{zenity.DefaultDate(2000, 1, 1)}},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := zenity.Calendar(fmt.Sprintf("Please, %s.", tt.call), tt.opts...)
+			if skip, err := skip(err); skip {
+				t.Skip("skipping:", err)
+			}
+			got.Date()
+			if !DateEquals(got, tt.want) || err != tt.err {
+				t.Errorf("Calendar() = %v, %v; want %v, %v", got, err, tt.want, tt.err)
+			}
+		})
+	}
+}
+
+func DateEquals(t1, t2 time.Time) bool {
+	d1, m1, y1 := t1.Date()
+	d2, m2, y2 := t2.Date()
+	return d1 == d2 && m1 == m2 && y1 == y2
+}
diff --git a/msg_test.go b/msg_test.go
index fca4554..4983438 100644
--- a/msg_test.go
+++ b/msg_test.go
@@ -43,7 +43,7 @@ func ExampleQuestion() {
 func ExampleCustomIcon() {
 	zenity.Info("All updates are complete.",
 		zenity.Title("Information"),
-		zenity.CustomIcon("./testdata/icon.png"))
+		zenity.CustomIcon("testdata/icon.png"))
 	// Output:
 }
 
diff --git a/util_windows.go b/util_windows.go
index 6752f94..43e8046 100644
--- a/util_windows.go
+++ b/util_windows.go
@@ -248,6 +248,8 @@ func saveBackRef(id uintptr, ptr unsafe.Pointer) {
 	defer backRefs.Unlock()
 	if backRefs.m == nil {
 		backRefs.m = map[uintptr]unsafe.Pointer{}
+	} else if _, ok := backRefs.m[id]; ok {
+		panic("saveBackRef")
 	}
 	backRefs.m[id] = ptr
 }