diff --git a/defaultcookiename.go b/defaultcookiename.go
index 5f13003..e30c5fc 100644
--- a/defaultcookiename.go
+++ b/defaultcookiename.go
@@ -11,18 +11,22 @@ import (
 var DefaultCookieName string
 
 func init() {
-	DefaultCookieName = "jaws"
-	if s, err := os.Executable(); err == nil {
-		s = filepath.Base(s)
-		s = strings.TrimSuffix(s, filepath.Ext(s))
-		var b []byte
-		for _, ch := range s {
-			if ('a' <= ch && ch <= 'z') || ('A' <= ch && ch <= 'Z') || ('0' <= ch && ch <= '9') {
-				b = append(b, byte(ch))
-			}
-		}
-		if len(b) > 0 {
-			DefaultCookieName = s
+	exename, _ := os.Executable()
+	DefaultCookieName = makeCookieName(exename)
+}
+
+func makeCookieName(exename string) (cookie string) {
+	cookie = "jaws"
+	exename = filepath.Base(exename)
+	exename = strings.TrimSuffix(exename, filepath.Ext(exename))
+	var b []byte
+	for _, ch := range exename {
+		if ('a' <= ch && ch <= 'z') || ('A' <= ch && ch <= 'Z') || ('0' <= ch && ch <= '9') {
+			b = append(b, byte(ch))
 		}
 	}
+	if len(b) > 0 {
+		cookie = string(b)
+	}
+	return
 }
diff --git a/defaultcookiename_test.go b/defaultcookiename_test.go
new file mode 100644
index 0000000..584be92
--- /dev/null
+++ b/defaultcookiename_test.go
@@ -0,0 +1,27 @@
+package jaws
+
+import (
+	"path"
+	"testing"
+)
+
+func Test_makeCookieName(t *testing.T) {
+	tests := []struct {
+		name       string
+		exename    string
+		wantCookie string
+	}{
+		{"empty string", "", "jaws"},
+		{"Simple", "Simple", "Simple"},
+		{"suffix.ed", "suffix.ed", "suffix"},
+		{"path", path.Join("c:", "path", "file.ext"), "file"},
+		{"invalid chars", " !??_", "jaws"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if gotCookie := makeCookieName(tt.exename); gotCookie != tt.wantCookie {
+				t.Errorf("makeCookieName() = %v, want %v", gotCookie, tt.wantCookie)
+			}
+		})
+	}
+}