AWS golang lambdaiface usage for testing lambda

Question

I'm trying to unit test a lambda function. Looking at the docs (https://docs.aws.amazon.com/sdk-for-go/api/service/lambda/lambdaiface) I'm not sure how to achieve it. The example given is non working and I cannot see any other usage of it. Particularly confusing to me is

func myFunc(svc lambdaiface.LambdaAPI) bool {
    // Make svc.AddLayerVersionPermission request
}

as AddLayerVersionPermission does not return a bool so again I'm confused with expected usage. I'm also unsure if I'm meant to mock out every function individually which would be tedious. Can anyone give me any pointers or working examples? Ultimately I only want to mock out Invoke()

Thanks

I tried reading the documentation but it was unclear to me.

could you please add more information on what did your function look like before introducing lambdaiface usage and the version of AWS SDK that you are using? — Emin Laletovic
– Emin Laletovic, Commented Apr 6, 2022 at 11:09
I haven't introduced it yet as I'm trying to build it test driven. I am trying to work out from the doc how I would do that. I am using v1.42.25 — GC30
– GC30, Commented Apr 6, 2022 at 11:21
This answer of mine should help you: stackoverflow.com/a/65466206/190823 — Jens
– Jens, Commented Apr 6, 2022 at 12:36

GC30 · Accepted Answer · 2022-04-06 14:16:09Z

That the documentations has a unneccessary boolean return from myFunc() threw me on how this worked. A colleague https://stackoverflow.com/users/966860/nathj07 got me through this. This is the full solution he helped me get

package main

import (
    "github.com/aws/aws-sdk-go/aws"
    "github.com/aws/aws-sdk-go/service/lambda"
    "github.com/aws/aws-sdk-go/service/lambda/lambdaiface"
    "github.com/stretchr/testify/mock"
)

type MockLambdaClient struct {
    mock.Mock
    lambdaiface.LambdaAPI
}

func (mlc *MockLambdaClient) Invoke(input *lambda.InvokeInput) (*lambda.InvokeOutput, error) {
    args := mlc.Called(input)
    return args.Get(0).(*lambda.InvokeOutput), args.Error(1)
}

type app struct {
    lambdaClient lambdaiface.LambdaAPI
}

func (a *app) invokeTest() {
    _, err := a.lambdaClient.Invoke(&lambda.InvokeInput{
        FunctionName: aws.String("a func name"),
        Payload:      []byte("the bytes"),
    })
    if err != nil {
        panic(err)
    }
}

func main() {

}

and the tests

package main

import (
    "testing"

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

func TestExample(t *testing.T) {
    mockLambda := &MockLambdaClient{}
    defer mockLambda.AssertExpectations(t)

    expInput := &lambda.InvokeInput{
        FunctionName: aws.String("a func name"),
        Payload:      []byte("the bytes"),
    }
    mockLambda.On("Invoke", expInput).Return(&lambda.InvokeOutput{}, nil).Times(1)

    a := app{}
    a.lambdaClient = mockLambda
    a.invokeTest()
}

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