It would appear that ShellServerIT was depending on seeing the ExampleShellExtension that was included in examples/simple.
As the examples no longer exist in the main tree, the test now fails in master.
Tests run: 49, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 119.224 sec <<< FAILURE! - in org.apache.accumulo.test.ShellServerIT
extensions(org.apache.accumulo.test.ShellServerIT) Time elapsed: 0.058 sec <<< FAILURE!
ExampleShellExtension present in root@miniInstance> extensions -l
was not true expected:<true> but was:<false>
Reproducible on master via mvn clean verify -Dtest=foo -Dit.test=ShellServerIT -Dcheckstyle.skip -Dfindbugs.skip.
Assigned this to you Mike Walch assuming that it was caused by
ACCUMULO-4511. Sorry if my assessment is wrong.