Upgrade to Hamcrest 2.1

[ankurpathak]

Spring Boot Starter Test still uses old Hamcrest 1.3. Now Hamcrest 2.1 released after 3 years and have many new matchers, so it make sense to use it in Spring Boot Starter Test, Please check this url
for more details:
hamcrest/JavaHamcrest#224

[wilkinsona]

so it make sense to use it in Spring Boot Starter Test

Thanks for the suggestion, but I'm not sure that it makes sense, at least not without considering other dependencies.

JUnit 4.12 depends on Hamcrest 1.3. We'd either need to be certain that it is compatible with 2.1 or consider the Hamcrest upgrade alongside a switch to JUnit 5 (version 5 dropped JUnit's Hamcrest dependency).

[wilkinsona]

Let's consider this in 2.2.x alongside #14736.

[wilkinsona]

This may still be blocked. While we have upgraded to JUnit 5 in spring-boot-starter-test, to allow users to gently migrate to it, we provide JUnit's Vintage Engine and the JUnit 4 API in the starter. Unfortunately, this means that Hamcrest 1.3 is still pulled in.

@sbrannen Do you know if JUnit 4, when being used "just" as an API on top of the Vintage Engine, requires Hamcrest 1.3, or can we exclude it and upgrade to 2.1?