When you apply multiple transformations, you run into a bug with the operator where the t0,t1 isn't applied like it should be. There is something wrong with String.join(","). Realistically we just need to add a comma between.

Also fixes the incorrect test so we can validate this better moving forward.

Real World Example

1 Transformation ✅
debezium.transforms.t0.negate=true
debezium.transforms.t0.predicate=TopicNameMatches
debezium.transforms.t0.topic.regex=<redacted>
debezium.transforms.t0.topic.replacement=<redacted>
debezium.transforms.t0.type=io.debezium.transforms.ByLogicalTableRouter
debezium.transforms=t0
 
When you have multiple transformations ❌
debezium.transforms.t0.negate=false
debezium.transforms.t0.predicate=TopicNameMatches
debezium.transforms.t0.type=<custom transform>
debezium.transforms.t1.negate=false
debezium.transforms.t1.predicate=TopicNameMatches
debezium.transforms.t1.regex=<redacted>
debezium.transforms.t1.replacement=<redacted
debezium.transforms.t1.type=org.apache.kafka.connect.transforms.RegexRouter
debezium.transforms.t2.negate=false
debezium.transforms.t2.predicate=TopicNameMatches
debezium.transforms.t2.type=<custom transform>
debezium.transforms.t3.negate=false
debezium.transforms.t3.predicate=TopicNameMatches
debezium.transforms.t3.type=<custom transform>
debezium.transforms=

Note the debezium.transforms is empty in the second example

What Debezium connector do you use and what version?

Not applicable

What is the connector configuration?

Posted above

What is the captured database version and mode of depoyment?

Not applicable

What behaviour do you expect?

I'd expect transforms to be populated

What behaviour do you see?

With multiple transforms it isn't populated

Do you see the same behaviour using the latest relesead Debezium version?

Yes

Do you have the connector logs, ideally from start till finish?

Not applicable

How to reproduce the issue using our tutorial deployment?

Not applicable