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: contract_test.go
    path of file: ./repos/syncthing/lib/ur/contract
    
    the code of the file until where you have to start completion: // Copyright (C) 2020 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at https://mozilla.org/MPL/2.0/.

package contract

import (
	"reflect"
	"testing"
)

type PtrStruct struct {
	A string         `since:"2"`
	B map[string]int `since:"3"`
}

type Nested struct {
	A float32 `since:"4"`
	B [4]int  `since:"5"`
	C bool    `since:"1"`
}

type TestStruct struct {
	A      int
	B      map[string]string `since:"1"`
	C      []string          `since:"2"`
	Nested Nested            `since:"3"`

	Ptr *PtrStruct `since:"2"`
}

func testValue() TestStruct {
	return TestStruct{
		A: 1,
		B: map[string]string{
			"foo": "bar",
		},
		C: []string{"a", "b"},
		Nested: Nested{
			A: 0.10,
			B: [4]int{1, 2, 3, 4
    
func TestClean(t *testing.T) {
	expect(t, 0, TestStruct{})

	expect(t, 1, TestStruct{
		// A unset, since it does not have "since"
		B: map[string]string{
			"foo": "bar",
		},
	})

	expect(t, 2, TestStruct{
		// A unset, since it does not have "since"
		B: map[string]string{
			"foo": "bar",
		},
		C: []string{"a", "b"},
		Ptr: &PtrStruct{
			A: "value",
		},
	})

	expect(t, 3, TestStruct{
		// A unset, since it does not have "since"
		B: map[string]string{
			"foo": "bar",
		},
		C: []string{"a", "b"},
		Nested: Nested{
			C: true,
		},
		Ptr: &PtrStruct{
			A: "value",
			B: map[string]int{
				"x": 1,
				"b": 2,
			},
		},
	})

	expect(t, 4, TestStruct{
		// A unset, since it does not have "since"
		B: map[string]string{
			"foo": "bar",
		},
		C: []string{"a", "b"},
		Nested: Nested{
			A: 0.10,
			C: true,
		},
		Ptr: &PtrStruct{
			A: "value",
			B: map[string]int{
				"x": 1,
				"b": 2,
			},
		},
	})

	x := testValue()
	x.A = 0

	expect(t, 5, x)
	expect(t, 6, x)
}