Even 2.5 make problems, see camunda/camunda-bpm-assert#90. Seems only 1.7.1 is safe so far.

I am upgrading to Camunda 7.8.0ee + Camunda Spring Boot Starter 2.3.0.
I'd really like to upgrade AssertJ too, but Camunda i holding us back.

So here is hoping that you will upgrade https://github.com/camunda/camunda-bpm-assert and get 2.0.0 released.
You don't have to worry that much about backwards compatibility, you can always release a 1.3.x branch.

We are on Java 8, so AssertJ 3.9+ might be preferable. But if it makes sense to stick with 2.6+ go with that.

I am currently testing with this fork. I looks like it works.
https://github.com/lldata/camunda-bpm-assert

I have not explored staying on jre7 or upgrading to 3.9.x

see the discussion on https://github.com/camunda/camunda-bpm-assert/issues/90

assertj > 3.0 requires Java8. So its not done with releasing camunda-bpm-assert 2.0, we need a version of this extension that is build with java 8. Maybe we could just have a camunda-bpm-assert-jdk8 module that rebuilds the sources.
However, since spring boot test < 2.x still relies on java 7, its default assertj version is 2.5 and you will have to manually exclude and overwrite the dependency.

The current camunda-bpm-spring-boot-starter-test uses assertj 2.x already by downloading the sources and rebuilding the module. You can easily do something similar in your project and just rebuild a local test module containing the sources.

Spring Boot 2.x support for the camunda starter will probably come with 7.9, then, with java8 as a default, this hopefully will work out of the box.

Still we could release 1.3 as java7 and assertJ 2.6 and a 2.0 with java8 and assertJ 3.9?
Even though we use java 8 I was reluctant to upgrade to 3.9, since we don't need it and spring still uses assertJ 2.x.

I think it is a lot of work to put on Camunda users that they have to build their own version of this lib. So I still think that something should be done other than waiting for 7.9 / Spring 2.0 / Java 8

You have to keep in mind that camunda-bpm-assert is not an official camunda product, it is a community extension (though a widely used and quite successful one), so there is no official support. We need to discuss this here https://github.com/camunda/camunda-bpm-assert/issues/90 and find a solution with the maintainer Martin Schimak. In the past he had concerns against switching java versions and loosening backward compatibility.
But I am with you: using the 2.0 release for a clean cut would be a nice solution (yet it will still have problems with spring-boot-test < 2.x).

FYI, camunda-bpm-assert dependency was removed from starter-test module, as it is not used in Spring Boot Starter test suite. Now developers are free to use any version of camunda-bpm-assert or AssetJ they need in their projects by directly including them in their project POMs.

Will close this ticket as not relevant anymore for Camunda Spring Boot Starter. The question of AssertJ version upgrade inside camunda-bpm-asser should be discussed in https://github.com/camunda/camunda-bpm-assert/issues/90 .