An `aws_rds_instance` resource block uses resource parameters to search for an RDS instance, and then tests that RDS instance. If no RDS instances match, no error is raised, but the `exists` matcher will return `false` and all properties will be `nil`. If more than one RDS instance matches (due to vague search parameters), an error is raised.
# Ensure you have a RDS instance with a certain ID
# This is "safe" - RDS IDs are unique within an account
describe aws_rds_instance('test-instance-id') do
it { should exist }
end
# Ensure you have a RDS instance with a certain ID
# This uses hash syntax
describe aws_rds_instance(db_instance_identifier: 'test-instance-id') do
Your [Principal](https://docs.aws.amazon.com/IAM/latest/UserGuide/intro-structure.html#intro-structure-principal) will need the `rds:DescribeDBInstances` action with Effect set to Allow.
You can find detailed documentation at [Actions, Resources, and Condition Keys for Amazon RDS](https://docs.aws.amazon.com/IAM/latest/UserGuide/list_amazonrds.html).