The issue is due to https://github.com/apache/zookeeper/blob/branch-3.6/zookeeper-server/src/test/java/org/apache/zookeeper/server/TxnLogCountTest.java

import static org.junit.jupiter.api.Assertions.assertEquals;

Cause the compilation error, since Junit 4 still in used.

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.1:testCompile ( default -testCompile) on project zookeeper: Compilation failure: Compilation failure: