There are several failing cases when executing the unit tests with Spark 2.2:
All of these are related to fixes/changes in Spark.
TestAssert, TestScalarAliases and TestEvalPipeline2 failures could be fixed by asserting on the message of the exception's root cause, looks like on Spark 2.2 the exception is wrapped into an additional layer.
TestStore and TestStoreLocal failure are also a test related problems: looks like
SPARK-7953 is fixed in Spark 2.2
The root cause of TestStoreInstances is yet to be found out.