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: stringfuncs_contrib_test.go
    path of file: ./repos/minio/internal/s3select/sql
    
    the code of the file until where you have to start completion: /*
 * MinIO Object Storage (c) 2021 MinIO, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 
    
func TestEvalSQLSubstring(t *testing.T) {
	evalCases := []struct {
		s           string
		startIdx    int
		length      int
		resExpected string
		errExpected error
	}{
		{"abcd", 1, 1, "a", nil},
		{"abcd", -1, 1, "a", nil},
		{"abcd", 999, 999, "", nil},
		{"", 999, 999, "", nil},
		{"测试abc", 1, 1, "测", nil},
		{"测试abc", 5, 5, "c", nil},
	}

	for i, tc := range evalCases {
		res, err := evalSQLSubstring(tc.s, tc.startIdx, tc.length)
		if res != tc.resExpected || err != tc.errExpected {
			t.Errorf("Eval Case %d failed: %v %v", i, res, err)
		}
	}
}