the `aws_iam_group_membership` resource
```
% make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSGroupMembership_'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
TF_ACC=1 go test ./builtin/providers/aws -v
-run=TestAccAWSGroupMembership_ -timeout 120m
=== RUN TestAccAWSGroupMembership_basic
--- PASS: TestAccAWSGroupMembership_basic (74.14s)
=== RUN TestAccAWSGroupMembership_paginatedUserList
--- PASS: TestAccAWSGroupMembership_paginatedUserList (273.29s)
PASS
ok github.com/hashicorp/terraform/builtin/providers/aws 347.447s
```
