looks good, why doesn't CI tests for Spark 2.1 fails for this?

would be great to understand why it worked before, but might merge this fix first.
merging if no more comment

I don't know either，It fails with spark 1.6.1.
May be the class check is still needed by 1.6,1?I'm not sure.
How can I trigger the build once more on travis-cli?

I don't think we need to check for all 3 classes, so I believe this fix is good.
what I don't understand is why it is failing for you but running just fine in travis CI where we have tests for Spark 2.1 - which is why I'm asking.

to trigger test, close this PR and reopen it.

e...
It works on my local mac with spark 2.1.0.
And pass the build with 2.1.0.
I seems that the build fails with
{code}
"env": "PYTHON="2" SCALA_VER="2.10" SPARK_VER="1.6.1" HADOOP_VER="2.6" PROFILE="-Pspark-1.6 -Phadoop-2.6 -Ppyspark" BUILD_FLAG="package -pl spark,python -am -DskipTests -DskipRat" TEST_FLAG="verify -DskipRat" TEST_PROJECTS="-pl zeppelin-interpreter,zeppelin-display,spark-dependencies,spark,python -Dtest=org.apache.zeppelin.spark.PySparkTest,org.apache.zeppelin.python. -Dpyspark.test.exclude='' -DfailIfNoTests=false"",
{code}

I think we'd better reopen the PR and build once more.
Maybe the class check is still necessary for spark 1.6.1

it's only the python2 + spark 1.6 profile. It ran fine with the other spark 1.6 profile so I think we are good.