You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: gutil_z_unit_struct_test.go
    path of file: ./repos/gf/util/gutil
    
    the code of the file until where you have to start completion: // Copyright GoFrame Author(https://goframe.org). All Rights Reserved.
//
// This Source Code Form is subject to the terms of the MIT License.
// If a copy of the MIT was not distributed with this file,
// You can obtain one at https://github.com/gogf/gf.

package gutil_test

import (
	"testing"

	"github.com/gogf/gf/v2/frame/g"
	"github.com/gogf/gf/v2/test/gtest"
	"github.com/gogf/gf/v2/util/gutil"
)

func Test_StructToSlice(t *testi
    
func Test_FillStructWithDefault(t *testing.T) {
	gtest.C(t, func(t *gtest.T) {
		type myInt int
		type Inner1 struct {
			I1V1 int
			I1V2 bool `d:"true"`
		}
		type Inner2 struct {
			I2V1 float64 `d:"1.01"`
		}
		type Inner3 struct {
			Inner1 Inner1
			I3V1   myInt `d:"1"`
		}
		type Inner4 struct {
		}
		type Outer struct {
			O1 int     `d:"1.01"`
			O2 string  `d:"1.01"`
			O3 float32 `d:"1.01"`
			*Inner1
			O4 bool `d:"true"`
			Inner2
			Inner3 Inner3
			Inner4 *Inner4
		}

		outer := Outer{}
		err := gutil.FillStructWithDefault(&outer)
		t.AssertNil(err)

		t.Assert(outer.O1, 1)
		t.Assert(outer.O2, `1.01`)
		t.Assert(outer.O3, `1.01`)
		t.Assert(outer.O4, true)
		t.Assert(outer.Inner1, nil)
		t.Assert(outer.Inner2.I2V1, `1.01`)
		t.Assert(outer.Inner3.I3V1, 1)
		t.Assert(outer.Inner3.Inner1.I1V1, 0)
		t.Assert(outer.Inner3.Inner1.I1V2, true)
		t.Assert(outer.Inner4, nil)
	})
}