Testing Against AWS APIs in Go

Testing code that accesses AWS can seem impossible, but it’s really not that hard! Let’s take a look at how we can use Go’s features to write useful tests for this kind of code, without a whole lot of work.

Transcript

1. Testing Against AWS APIs With Go Steve Scaffidi
 HERE Technologies Github/Twitter: @hercynium
2. Testing live systems is challenging
3. You do test, right?
4. Mock AWS* *neener, neener, neener!
5. func main() { awsSess, e := awsSession.NewSession() kingpin.FatalIfError(e, "Could not create AWS API session") instanceIds := GetAwsInstanceIds(awsSess) for _, id := range instanceIds { fmt.Println(id) } } func GetAwsInstanceIds(awsSess *awsSession.Session) []string { instanceIds := make([]string, 0) ec2Api := ec2.New(awsSess) instDescrs, err := ec2Api.DescribeInstances(&ec2.DescribeInstancesInput{}) kingpin.FatalIfError(err, "Could not get EC2 instances") for _, res := range instDescrs.Reservations { for _, instance := range res.Instances { instanceIds = append(instanceIds, *instance.InstanceId) } } return instanceIds }
6. func main() { awsSess, e := awsSession.NewSession() kingpin.FatalIfError(e, "Could not create AWS API session") instanceIds := GetAwsInstanceIds(awsSess) for _, id := range instanceIds { fmt.Println(id) } } func GetAwsInstanceIds(awsSess *awsSession.Session) []string { instanceIds := make([]string, 0) ec2Api := ec2.New(awsSess) instDescrs, err := ec2Api.DescribeInstances(&ec2.DescribeInstancesInput{}) kingpin.FatalIfError(err, "Could not get EC2 instances") for _, res := range instDescrs.Reservations { for _, instance := range res.Instances { instanceIds = append(instanceIds, *instance.InstanceId) } } return instanceIds }
7. func main() { awsSess, e := awsSession.NewSession() kingpin.FatalIfError(e, "Could not create AWS API session") instanceIds := GetAwsInstanceIds(awsSess) for _, id := range instanceIds { fmt.Println(id) } } func GetAwsInstanceIds(awsSess *awsSession.Session) []string { instanceIds := make([]string, 0) ec2Api := ec2.New(awsSess) instDescrs, err := ec2Api.DescribeInstances(&ec2.DescribeInstancesInput{}) kingpin.FatalIfError(err, "Could not get EC2 instances") for _, res := range instDescrs.Reservations { for _, instance := range res.Instances { instanceIds = append(instanceIds, *instance.InstanceId) } } return instanceIds }
9. DescribeInstances(*ec2.DescribeInstancesInput) (*ec2.DescribeInstancesOutput, error) From: https://godoc.org/github.com/aws/aws-sdk-go/service/ec2/ec2iface
11. func main() { awsSess, e := awsSession.NewSession() kingpin.FatalIfError(e, "Could not create AWS API session") instanceIds := GetAwsInstanceIds(awsSess) for _, id := range instanceIds { fmt.Println(id) } } func GetAwsInstanceIds(awsSess *awsSession.Session) []string { instanceIds := make([]string, 0) ec2Api := ec2.New(awsSess) instDescrs, err := ec2Api.DescribeInstances(&ec2.DescribeInstancesInput{}) kingpin.FatalIfError(err, "Could not get EC2 instances") for _, res := range instDescrs.Reservations { for _, instance := range res.Instances { instanceIds = append(instanceIds, *instance.InstanceId) } } return instanceIds }
12. Mock the Client APIs
13. ec2.EC2 --> ec2iface.EC2API
14. func main() { awsSess, e := awsSession.NewSession() kingpin.FatalIfError(e, "Could not create AWS API session") ec2Api := ec2.New(awsSess) instanceIds := GetAwsInstanceIds(ec2Api) for _, id := range instanceIds { fmt.Println(id) } } func GetAwsInstanceIds(ec2Api ec2iface.EC2API) []string { instanceIds := make([]string, 0) instDescrs, err := ec2Api.DescribeInstances(&ec2.DescribeInstancesInput{}) kingpin.FatalIfError(err, "Could not get EC2 instances") for _, res := range instDescrs.Reservations { for _, instance := range res.Instances { instanceIds = append(instanceIds, *instance.InstanceId) } } return instanceIds }
15. func main() { awsSess, e := awsSession.NewSession() kingpin.FatalIfError(e, "Could not create AWS API session") ec2Api := ec2.New(awsSess) instanceIds := GetAwsInstanceIds(ec2Api) for _, id := range instanceIds { fmt.Println(id) } } func GetAwsInstanceIds(ec2Api ec2iface.EC2API) []string { instanceIds := make([]string, 0) instDescrs, err := ec2Api.DescribeInstances(&ec2.DescribeInstancesInput{}) kingpin.FatalIfError(err, "Could not get EC2 instances") for _, res := range instDescrs.Reservations { for _, instance := range res.Instances { instanceIds = append(instanceIds, *instance.InstanceId) } } return instanceIds }
16. func main() { awsSess, e := awsSession.NewSession() kingpin.FatalIfError(e, "Could not create AWS API session") ec2Api := ec2.New(awsSess) instanceIds := GetAwsInstanceIds(ec2Api) for _, id := range instanceIds { fmt.Println(id) } } func GetAwsInstanceIds(ec2Api ec2iface.EC2API) []string { instanceIds := make([]string, 0) instDescrs, err := ec2Api.DescribeInstances(&ec2.DescribeInstancesInput{}) kingpin.FatalIfError(err, "Could not get EC2 instances") for _, res := range instDescrs.Reservations { for _, instance := range res.Instances { instanceIds = append(instanceIds, *instance.InstanceId) } } return instanceIds }
17. func makeInstance(instanceId string) *ec2.Instance { return &ec2.Instance{InstanceId: aws.String(instanceId)} } func makeDescribeInstancesOutput(instanceIds []string)
 *ec2.DescribeInstancesOutput { instances := make([]*ec2.Instance, 0) for _, id := range instanceIds { instances = append(instances, makeInstance(id)) } return &ec2.DescribeInstancesOutput{ Reservations: []*ec2.Reservation{ { Instances: instances, }, }, } }
18. type testAwsEc2API struct { ec2iface.EC2API instanceIds []string } func (d testAwsEc2API) DescribeInstances(input *ec2.DescribeInstancesInput) (*ec2.DescribeInstancesOutput, error) { return makeDescribeInstancesOutput(d.instanceIds), nil }
19. type testAwsEc2API struct { ec2iface.EC2API instanceIds []string } func (d testAwsEc2API) DescribeInstances(input *ec2.DescribeInstancesInput) (*ec2.DescribeInstancesOutput, error) { return makeDescribeInstancesOutput(d.instanceIds), nil }
20. func Test_GetAwsInstanceIds(t *testing.T) { tests := []struct { name string instanceIds []string }{ { name: "get all instance IDs", instanceIds:
 []string{"i-11111", "i-22222", "i-33333"}, }, } for _, test := range tests { t.Run(test.name, func(t *testing.T) { ec2API := &testAwsEc2API{ instanceIds: test.instanceIds, } gotInstanceIds := GetAwsInstanceIds(ec2API) assert.Equal(t, test.instanceIds, gotInstanceIds) }) } }
21. func Test_GetAwsInstanceIds(t *testing.T) { tests := []struct { name string instanceIds []string }{ { name: "get all instance IDs", instanceIds:
 []string{"i-11111", "i-22222", "i-33333"}, }, } for _, test := range tests { t.Run(test.name, func(t *testing.T) { ec2API := &testAwsEc2API{ instanceIds: test.instanceIds, } gotInstanceIds := GetAwsInstanceIds(ec2API) assert.Equal(t, test.instanceIds, gotInstanceIds) }) } }
22. Time for a live demo?
23. Thank You!