Move waitForTable to DynamoDb.WaitForTable

This method was originally only a test helper, but we need it for the
upcoming 'elistman create-subscribers-table' command. This is because
we'll need to wait for the table before calling UpdateTimeToLive.

db/dynamodb.go

@@ -130,6 +130,15 @@ func (db *DynamoDb) CreateTable(ctx context.Context) (err error) {
 	return
 }
 
+func (db *DynamoDb) WaitForTable(
+	ctx context.Context, maxWait time.Duration,
+) error {
+	input := &dynamodb.DescribeTableInput{TableName: aws.String(db.TableName)}
+	waiter := dynamodb.NewTableExistsWaiter(db.Client)
+
+	return waiter.Wait(ctx, input, maxWait)
+}
+
 func (db *DynamoDb) UpdateTimeToLive(
 	ctx context.Context,
 ) (ttlSpec *dbtypes.TimeToLiveSpecification, err error) {

db/dynamodb_contract_test.go

@@ -67,7 +67,7 @@ func setupDynamoDb() (dynDb *DynamoDb, teardown func() error, err error) {
 		return
 	} else if err = dynDb.CreateTable(ctx); err != nil {
 		err = teardownDbWithError(err)
-	} else if err = waitForTable(ctx, dynDb); err != nil {
+	} else if err = dynDb.WaitForTable(ctx, maxTableWaitDuration); err != nil {
 		err = teardownDbWithError(err)
 	} else {
 		teardown = func() error {
@@ -138,15 +138,6 @@ func localDbConfig() (*aws.Config, string, error) {
 	return dbConfig, endpoint, nil
 }
 
-func waitForTable(ctx context.Context, dynDb *DynamoDb) error {
-	input := &dynamodb.DescribeTableInput{
-		TableName: aws.String(dynDb.TableName),
-	}
-	waiter := dynamodb.NewTableExistsWaiter(dynDb.Client)
-
-	return waiter.Wait(ctx, input, maxTableWaitDuration)
-}
-
 func newTestSubscriber() *Subscriber {
 	return NewSubscriber(testutils.RandomString(8) + "@example.com")
 }