For people who might find this bug, and aren't on Slack: the (shaded) org.testcontainers.shaded.com.fasterxml.jackson.databind.introspect.JacksonAnnotationIntrospector has references to (non-shaded) com.fasterxml.jackson.annotation.*.

A band-aid for our usecase was to add jackson-annotations:2.9.0 on the test classpath – TestContainers 1.15.1 includes jackson-databind:2.8.8, but the JacksonAnnotationIntrospector references the JsonMerge annotation which wasn't added before 2.9.0 🤔

The non-shaded reference isn't a problem, actually.

The actual issue comes from the fact that Jackson Databind 2.9+ does not work with annotations 2.8 and requires them to be 2.9 or higher.