spring boot starter test 1.4.1 - use assertj-core 3.5.x - maven

Question

I want to use the latest assertj-core for Java8 (for example to assert on optionals).
I use spring-boot-starter-test 1.4.1 it comes with assertj 2.5.0 preconfigured.
I cannot use a spring boot parent pom.
How can I set up my maven project, so I exclude or overwrite version 2.5.0 with 3.5.2? I tried
setting just the property assertj.version
adding exclusions on the starter-test dependency
adding exclusion on the spring-boot-dependencies
Update:
I am setting up a custom "test" module for all modules in my multi module project. I do not just need spring-test-starter but also some other dependencies and some test classes and rules.
This is what my project looks like:
my-module-root
|-my-module-a (using test)
|-my-module-b (using test)
\-test (including starter-test, ... - in COMPILE scope (because this is a test library))
Now, when I exclude assertj-core on the test module (and include 3.5.2), the dependencies for the test module are ok.
But when I check the dependencies on the root level, I have both, assertj-core-2.5.0 and assertj-core-3.5.2 on the classpath.

Answer 1

You can exclude it from spring-boot-starter-test and then add manually different version:
<dependencies>
...
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
<exclusions>
<exclusion>
<groupId>org.assertj</groupId>
<artifactId>assertj-core</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.assertj</groupId>
<artifactId>assertj-core</artifactId>
<version>3.5.2</version>
<scope>test</scope>
</dependency>
</dependencies>
To verify which version is included:
$ mvn dependency:tree | grep assertj
[INFO] \- org.assertj:assertj-core:jar:3.5.2:test