JupiterTestEngine crashes if JUnit 4 is on the classpath but Hamcrest is not

[sbrannen]

Overview

While migrating the Spring Framework test suite from JUnit 4 and Hamcrest to JUnit Jupiter and AssertJ, entire projects in Spring's test suite started reporting zero tests after removing the dependency on Hamcrest even though the tests no longer used Hamcrest. Adding Hamcrest back as a test runtime dependency allowed the tests to execute again.

Analysis

Thanks to some investigative work by @marcphilipp, we came to the following conclusion.

The JupiterTestEngine fails with a NoClassDefFoundError if JUnit 4 is on the classpath but Hamcrest is not. The underlying reason is that OpenTest4JAndJUnit4AwareThrowableCollector has a static initialization block that checks if the org.junit.internal.AssumptionViolatedException class can be loaded. However, since AssumptionViolatedException has a direct dependency on org.hamcrest.Matcher, a NoClassDefFoundError is thrown when attempting to load AssumptionViolatedException.

Deliverables

• Refactor OpenTest4JAndJUnit4AwareThrowableCollector so that a failed attempt to detect the presence of AssumptionViolatedException in the classpath does not crash the entire JupiterTestEngine.
• Document in the Release Notes.