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: builtin_string_test.go
    path of file: ./repos/tidb/pkg/expression
    
    the code of the file until where you have to start completion: // Copyright 2015 PingCAP, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// y
    
func TestUpper(t *testing.T) {
	ctx := createContext(t)
	cases := []struct {
		args   []any
		isNil  bool
		getErr bool
		res    string
	}{
		{[]any{nil}, true, false, ""},
		{[]any{"ab"}, false, false, "ab"},
		{[]any{1}, false, false, "1"},
		{[]any{"one weekâ€™s time TEST"}, false, false, "ONE WEEKâ€™S TIME TEST"},
		{[]any{"one week's time TEST"}, false, false, "ONE WEEK'S TIME TEST"},
		{[]any{"abcæµ‹è¯•def"}, false, false, "ABCæµ‹è¯•DEF"},
		{[]any{"abcãƒ†ã‚¹ãƒˆdef"}, false, false, "ABCãƒ†ã‚¹ãƒˆDEF"},
	}

	for _, c := range cases {
		f, err := newFunctionForTest(ctx, ast.Upper, primitiveValsToConstants(ctx, c.args)...)
		require.NoError(t, err)
		v, err := f.Eval(ctx, chunk.Row{})
		if c.getErr {
			require.Error(t, err)
		} else {
			require.NoError(t, err)
			if c.isNil {
				require.Equal(t, types.KindNull, v.Kind())
			} else {
				require.Equal(t, strings.ToUpper(c.res), v.GetString())
			}
		}
	}

	_, err := funcs[ast.Upper].getFunction(ctx, []Expression{getVarcharCon()})
	require.NoError(t, err)

	// Test GBK String
	tbl := []struct {
		input  string
		chs    string
		result string
	}{
		{"abc", "gbk", "ABC"},
		{"ä¸€äºŒä¸‰", "gbk", "ä¸€äºŒä¸‰"},
		{"Ã bc", "gbk", "Ã BC"},
		{"Ã Ã¡Ã¨Ã©ÃªÃ¬Ã­Ã²Ã³Ã¹ÃºÃ¼ÄÄ“Ä›Ä«Å„ÅˆÅÅ«ÇŽÇÇ’Ç”Ç–Ç˜ÇšÇœâ…ªâ…«", "gbk", "Ã Ã¡Ã¨Ã©ÃªÃ¬Ã­Ã²Ã³Ã¹ÃºÃ¼ÄÄ“Ä›Ä«Å„ÅˆÅÅ«ÇŽÇÇ’Ç”Ç–Ç˜ÇšÇœâ…ªâ…«"},
		{"Ã Ã¡Ã¨Ã©ÃªÃ¬Ã­Ã²Ã³Ã¹ÃºÃ¼ÄÄ“Ä›Ä«Å„ÅˆÅÅ«ÇŽÇÇ’Ç”Ç–Ç˜ÇšÇœâ…ªâ…«", "", "Ã€ÃÃˆÃ‰ÃŠÃŒÃÃ’Ã“Ã™ÃšÃœÄ€Ä’ÄšÄªÅƒÅ‡ÅŒÅªÇÇÇ‘Ç“Ç•Ç—Ç™Ç›â…ªâ…«"},
	}
	for _, c := range tbl {
		err := ctx.GetSessionVars().SetSystemVarWithoutValidation(variable.CharacterSetConnection, c.chs)
		require.NoError(t, err)
		f, err := newFunctionForTest(ctx, ast.Upper, primitiveValsToConstants(ctx, []any{c.input})...)
		require.NoError(t, err)
		d, err := f.Eval(ctx, chunk.Row{})
		require.NoError(t, err)
		require.Equal(t, c.result, d.GetString())
	}
}