Go create a mock for gcp compute sdk

Question

I use the following function, and I need to raise the coverage of it (if possible to 100%), the problem is that typically I use interface to handle such cases in Go and for this specific case not sure how to do it, as this is a bit more tricky, any idea?

The package https://pkg.go.dev/google.golang.org/genproto/googleapis/cloud/compute/v1

Which I use doesn't have interface so not sure how can I mock it?

import (
    "context"
    "errors"
    "fmt"
    "os"

    compute "cloud.google.com/go/compute/apiv1"
    "google.golang.org/api/iterator"
    "google.golang.org/api/option"
    computev1 "google.golang.org/genproto/googleapis/cloud/compute/v1"
)

func Res(ctx context.Context, project string, region string,vpc string,secret string) error {

    c, err := compute.NewAddressesRESTClient(ctx, option.WithCredentialsFile(secret))

    if err != nil {
        return err
    }

    defer c.Close()
    addrReq := &computev1.ListAddressesRequest{
        Project: project,
        Region:  region,
    }
    it := c.List(ctx, addrReq)

    for {
        resp, err := it.Next()
        if err == iterator.Done {
            break
        }
        if err != nil {
            return err
        }
        if *(resp.Status) != "IN_USE" {
            return ipConverter(*resp.Name, vpc)
        }
    }
    return nil
}

Answer 1

Whenever I find myself in this scenario, I found that the easiest solution is to create missing interfaces myself. I limit these interfaces to the types and functions that I am using, instead of writing interfaces for the entire library. Then, in my code, instead of accepting third-party concrete types, I accept my interfaces for those types. Then I use gomock to generate mocks for these interfaces as usual.

The following is a descriptive example inspired by your code.

type RestClient interface {
    List(context.Context, *computev1.ListAddressesRequest) (ListResult, error) // assuming List returns ListResult type.
    Close() error
}

func newRestClient(ctx context.Context, secret string) (RestClient, error) {
    return compute.NewAddressesRESTClient(ctx, option.WithCredentialsFile(secret))
}

func Res(ctx context.Context, project string, region string, vpc string, secret string) error {
    c, err := newRestClient(ctx, secret)
    if err != nil {
        return err
    }

    defer c.Close()
    return res(ctx, project, region, vpc, c)
}

func res(ctx context.Context, project string, region string, vpc string, c RestClient) error {
    addrReq := &computev1.ListAddressesRequest{
        Project: project,
        Region:  region,
    }

    it, err := c.List(ctx, addrReq)
    if err != nil {
        return err
    }

    for {
        resp, err := it.Next()
        if err == iterator.Done {
            break
        }

        if err != nil {
            return err
        }

        if *(resp.Status) != "IN_USE" {
            return ipConverter(*resp.Name, vpc)
        }
    }

    return nil
}

Now you can test the important bits of the Res function by injecting a mock RestClient to the internal res function.