refactor: organize plugin to support multiple services (#1)

Co-authored-by: Michael Li <michael.li@hashicorp.com>

internal/credential/testing.go

@@ -0,0 +1,47 @@
+package credential
+
+import (
+	"github.com/aws/aws-sdk-go/aws/session"
+	"github.com/aws/aws-sdk-go/service/iam"
+	"github.com/aws/aws-sdk-go/service/iam/iamiface"
+	"github.com/hashicorp/go-secure-stdlib/awsutil"
+)
+
+const (
+	testOptionErr            = "test option error"
+	testGetCallerIdentityErr = "test error for GetCallerIdentity"
+	testGetUserErr           = "test error for GetUser"
+	testDeleteAccessKeyErr   = "test error for DeleteAccessKey"
+)
+
+type testMockIAMState struct {
+	DeleteAccessKeyCalled bool
+}
+
+func (s *testMockIAMState) Reset() {
+	s.DeleteAccessKeyCalled = false
+}
+
+type testMockIAM struct {
+	iamiface.IAMAPI
+
+	State *testMockIAMState
+}
+
+func (m *testMockIAM) DeleteAccessKey(input *iam.DeleteAccessKeyInput) (*iam.DeleteAccessKeyOutput, error) {
+	m.State.DeleteAccessKeyCalled = true
+	return m.IAMAPI.DeleteAccessKey(input)
+}
+
+func newTestMockIAM(state *testMockIAMState, opts ...awsutil.MockIAMOption) awsutil.IAMAPIFunc {
+	return func(sess *session.Session) (iamiface.IAMAPI, error) {
+		m := &testMockIAM{
+			State: state,
+		}
+		f := awsutil.NewMockIAM(opts...)
+		var err error
+
+		m.IAMAPI, err = f(sess)
+		return m, err
+	}
+}