S3 Create bucket doesn't throw an error when bucket already exists

[ash-murphy-colibri]

Describe the bug

When running the s3 client's create bucket method no exception is thrown when the bucket already exists. I also tried changing the region from eu-west-1 to eu-west-2 (by using Loc. Constraints) but still no exception is being raised.

The image below is the unit test, you'll see in the console the bucket exists.

This is the code I would expect to throw an error:

      try:
        if deployment_region == "us-east-1":
            s3.create_bucket(ACL="private", Bucket=bucket_name)
        else:
            s3.create_bucket(
                ACL="private",
                Bucket=bucket_name,
                CreateBucketConfiguration={"LocationConstraint": deployment_region},
            )

Expected Behavior

I expected BucketAlreadyExists exception to be raised.

Current Behavior

No issues, response is 200.

Please note, this happens immediately after upgrading from version 4 to 5.0.14

Reproduction Steps

import boto3
from Moto import mock_aws   
   
    with mock_aws():
        s3 =  boto3.client("s3")
        s3.create_bucket(Bucket="my_bucket")
        s3.create_bucket(Bucket="my_bucket")

Possible Solution

Looking at the boto code it seems the check in create bucket should be:

def create_bucket(self, bucket_name: str, region_name: str) -> FakeBucket:
        if bucket_name in self.buckets:

Instead of:

def create_bucket(self, bucket_name: str, region_name: str) -> FakeBucket:
        if bucket_name in s3_backends.bucket_accounts.keys():

Additional Information/Context

Please see the preceding screenshots for more details.

You will see that list buckets queries the correct property but create bucket incorrectly queries a property with no buckets

SDK version used

5.0.14

Environment details (OS name and version, etc.)

Mac OS - 14.6.1. Python 3.9 (Anaconda env)

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