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: ConfigureFunction_test.go
    path of file: ./repos/aws-doc-sdk-examples/go/lambda/ConfigureFunction
    
    the code of the file until where you have to start completion: // Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: MIT-0

package main

import (
    "errors"
    "testing"
    "time"

    "github.com/aws/aws-sdk-go/service/lambda"
    "github.com/aws/aws-sdk-go/service/lambda/lambdaiface"
)

// Define a mock struct to use in unit tests
type mockLambdaClient struct {
    lambdaiface.LambdaAPI
}

func (m *mockLambdaCl
    
func (m *mockLambdaClient) AddPermission(input *lambda.AddPermissionInput) (*lambda.AddPermissionOutput, error) {
    // Check that required inputs exist
    if input.FunctionName == nil || *input.FunctionName == "" ||
        input.SourceArn == nil || *input.SourceArn == "" {
        return nil, errors.New("AddPermissionInput.FunctionName or AddPermissionInput.SourceArn is nil or an empty string")
    }

    resp := lambda.AddPermissionOutput{}
    return &resp, nil
}